Wireless device and wireless communication method

ABSTRACT

According to one embodiment, a wireless device includes a transmitter; and a receiver. The transmitter is configured to transmit a first frame including information that designates a plurality of frequency components and instructing execution of frequency multiplexing transmission by a plurality of wireless communication terminals; and the receiver is configured to receive the second frame by at least one frequency component of the plurality of frequency components. The first frame has either a first form or a second form, the first form designates individual terminal identifiers of the plurality of wireless communication terminals, the terminal identifiers each being associated with at least one of the plurality of frequency components, and the second form designates a group identifier of a group to which the plurality of wireless communication terminals belong.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/202,960, filed on Jul. 6, 2016, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2015-136480filed Jul. 7, 2015 and No. 2016-133604 filed Jul. 5, 2016; the entirecontents of all of the above applications are incorporated herein byreference.

FIELD

Embodiments of the present invention relate to a wireless device and awireless communication method.

BACKGROUND

Frequency multiplexing communication is known according to whichdifferent frequency components for each wireless communication terminal(hereinafter referred to as terminal) are used as communicationresources and transmissions to a plurality of terminals and receptionsfrom a plurality of terminals are simultaneously performed. Here,Orthogonal Frequency Division Multiple Access (OFDMA) scheme isconsidered where the frequency components are defined as resource unitseach including one or a plurality of subcarriers, and the resource unitseach are used as a smallest unit of the communication resource, andtransmissions to the plurality of terminals or receptions from theplurality of terminals are simultaneously performed. The simultaneoustransmissions from the base station to the plurality of terminalscorrespond to downlink OFDMA (DL-OFDMA) transmission and thesimultaneous transmissions from the plurality of terminals to the basestation correspond to uplink OFDMA (UL-OFDMA) transmission.

When uplink OFDMA (UL-OFDMA) communication is to be performed, it may beconsidered to transmit a trigger frame from a base station in order toalign the uplink transmission timings of the individual terminals. Thereis a method that notifies the information regarding the assignmentterminals on a per-resource-unit basis by the trigger frame, and therebydesignating the terminals that perform UL-OFDMA communication and theresource units to be used by the terminals. In accordance with thismethod, there is a problem of degradation in efficiency of utilizingcommunication resources in a case where a terminal has entered its sleepmode and in a case where there is no pending uplink transmission demandat a terminal. As another method, there is a method that does notperform designation of the terminals by the trigger frame but onlydesignates the resource units to be used. In this case, a terminal thathas received a trigger frame acquires a resource unit based on atechnique similar to random backoff procedure. At this point, when thereare a large number of terminals that have received the trigger frame,there is a high likelihood of the same resource unit being selected.When a plurality of terminals transmits frames using the same resourceunit, the base station cannot successfully receive the frames.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a wireless communication deviceaccording to an embodiment of the present invention;

FIG. 2 is a diagram for explanation of assignment of a resource unit;

FIGS. 3(A) to 3(C) are diagrams for explanation of variousconfigurations of the resource unit;

FIG. 4 is a diagram illustrating a wireless communication groupincluding a base station and a plurality of terminals;

FIGS. 5(A) and (B) are a diagram illustrating a basic exemplary formatof a MAC frame;

FIG. 6 is a diagram illustrating an exemplary format of an informationelement;

FIG. 7 is a diagram illustrating an operation sequence in accordancewith the present invention;

FIG. 8 is a diagram illustrating an exemplary format of a physicalpacket including a trigger frame;

FIGS. 9(A) and 9 (B) are diagrams illustrating an exemplary format ofthe trigger frame;

FIG. 10 is a diagram illustrating an exemplary configuration of anRU/AID field in the trigger frame.

FIG. 11 is a diagram illustrating another exemplary format of thetrigger frame;

FIG. 12 is a diagram illustrating another exemplary format of thetrigger frame;

FIG. 13 is a diagram illustrating another exemplary format of thetrigger frame;

FIG. 14 is a diagram illustrating another exemplary format of thetrigger frame;

FIG. 15 is a diagram illustrating another exemplary format of thetrigger frame;

FIG. 16 is a diagram illustrating another exemplary format of thetrigger frame;

FIG. 17 is a diagram illustrating another exemplary format of thetrigger frame;

FIG. 18 is a diagram illustrating a flowchart of an example of operationof the base station in accordance with the embodiment of the presentinvention;

FIG. 19 is a diagram for explanation of a channel for transmission ofthe trigger frame;

FIG. 20 is a diagram illustrating a flowchart of an example of operationof a terminal in accordance with the embodiment of the presentinvention;

FIG. 21 is a functional block diagram of a base station or a terminal inaccordance with a second embodiment;

FIG. 22 is a diagram illustrating an exemplary overall configuration ofa terminal or a base station in accordance with a third embodiment;

FIG. 23 is a diagram illustrating a hardware configuration of a wirelessLAN module incorporated in a terminal or a base station in accordancewith the third embodiment;

FIG. 24 is a perspective view of a wireless communication terminal inaccordance with the embodiment of the present invention;

FIG. 25 is a diagram illustrating a memory card in accordance with theembodiment of the present invention; and

FIG. 26 is a diagram illustrating an example of exchange of framesduring a contention period.

DETAILED DESCRIPTION

According to one embodiment, a wireless device includes a transmitter;and a receiver.

The transmitter is configured to transmit a first frame includinginformation that designates a plurality of frequency components andinstructing execution of frequency multiplexing transmission by aplurality of wireless communication terminals.

The receiver is configured to receive the second frame by at least onefrequency component of the plurality of frequency components.

The first frame has either a first form or a second form.

The first form designates individual terminal identifiers of theplurality of wireless communication terminals, the terminal identifierseach being associated with at least one of the plurality of frequencycomponents.

The second form designates a group identifier of a group to which theplurality of wireless communication terminals belong.

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The entire contents of IEEE Std 802.11™-2012and IEEE Std 802.11ac™-2013, known as the wireless LAN specification andIEEE 802.11-15/0132r17 dated May 25, 2016 which is SpecificationFramework Document directed to IEEE Std 802.11ax as a next generationwireless LAN standards are herein incorporated by reference in thepresent specification.

First Embodiment

A functional block diagram of a wireless communication device (or awireless device) according to the first embodiment of the presentinvention is illustrated in FIG. 1 . This wireless communication devicecan be implemented in a wireless communication base station (hereinafterreferred to as a base station or an access point) or in a wirelesscommunication terminal (hereinafter referred to as a terminal) thatcommunicates with the base station. The base station is one mode of theterminal in that the base station has the same or similar communicationfunctions with those of the terminal with exception of the base stationhaving a relay function. When a terminal is mentioned in the followingexplanations, it may refer to a base station as long as the terminal andthe base station should be particularly discriminated from each other.

This embodiment handles a case where uplink OFDMA (UL-OFDMA: OrthogonalFrequency Division Multiple Access) transmission is performed from aplurality of terminals to the base station. In UL-OFDMA, resource unitseach including one or a plurality of subcarriers are assigned toterminals (the resource unit may also be called subchannel, resourceblock, or frequency block), and receptions from the plurality ofterminals are performed simultaneously on resource unit basis. Theresource unit is a smallest unit of a resource for performingcommunication. FIG. 3 illustrates the resource units (RU #1, RU #2 . . .RU #K) arranged within a continuous frequency domain of one channel(which is described here as the channel M). A plurality of subcarriersorthogonal to each other are arranged in the channel M, and a pluralityof resource units including one or a plurality of continuous subcarriersare defined within the channel M. Although one or more subcarriers(guard subcarriers) may be arranged between the resource units, presenceof the guard subcarrier is not essential. A number for identification ofthe subcarrier or the resource unit may be assigned to each carrier oreach resource unit in the channel. The bandwidth of one channel may befor example, though not limited to these, 20 MHz, 40 MHz, 80 MHz, and160 MHz. One channel may be constituted by combining a plurality ofchannels of 20 MHz. The number of subcarriers in the channel or thenumber of resource units may vary in accordance with the bandwidth.Uplink OFDMA communication is realized by different resource units beingsimultaneously used by different terminals.

The bandwidths of the resource units (or the number of the subcarriers)may be same among the resource units, or the bandwidths (or the numberof the subcarriers) may vary depending on the individual resource units.An exemplary arrangement pattern of the resource units within onechannel is schematically illustrated in FIG. 3 . The width direction onthe paper surface corresponds to the frequency domain direction. FIG.3(A) illustrates an example where a plurality of resource units (RU #1,RU #2 RU #K) having the same bandwidth are arranged, and FIG. 3(B)illustrates another example where a plurality of resource units (RU#11-1, RU #11-2 . . . RU #11-L) having a larger bandwidth than that ofFIG. 3(A) are arranged. FIG. 3(C) illustrates a still another examplewhere resource units with three types of bandwidths are arranged. Theresource units (RU #12-1, RU #12-2) have the largest bandwidth, theresource unit RU #11-(L−1) has the bandwidth identical to that of FIG.3(B), and the resource units (RU #K−1, RU #K) have the bandwidthidentical to that of FIG. 3(A).

A specific example is illustrated. When the entire 20 MHz channel widthis used, 26 resource units (tones) may be specified for the 256subcarriers (tones) arranged within the 20 MHz channel width. In otherwords, nine resource units are specified in the 20 MHz channel width andthe bandwidth of the resource unit becomes smaller than the 2.5 MHzwidth. In the case of a 40 MHz channel width, 18 resource units arespecified therefor. In the case of an 80 MHz channel width, 37 resourceunits are specified (see doc.: IEEE 802.11-15/0330r5). When this isextended, for example, in the case of a 160 MHz channel width or an80+80 MHz channel width, 74 resource units are specified. It will beappreciated that the width of the resource unit is not limited to aparticular value and resource units of various sizes can be arranged.

Here, the number of resource units used by each terminal is not limitedto a particular value and one or a plurality of resource units may beused. When a terminal uses a plurality of resource units, a plurality ofresource units that are continuous in terms of frequency may be used, ora plurality of resource units that are located at positions away fromeach other may be allowed to be used.

It is assumed here that subcarriers within one resource unit arecontinuous in the frequency domain. However, resource units may bedefined with use of a plurality of subcarriers that are arranged in anon-continuous manner. The channels used in uplink OFDMA communicationare not limited to one single channel but resource units may be reservedin another channel (see the channel N in FIG. 2 , for example) arrangedat a location away in the frequency domain from the channel M as thecase of the channel M and thus the resource units in both the channel Mand the channel N may be used. The same or different modes of arrangingthe resource units may be used for the channel M and the channel N. Thebandwidth of the channel N is by way of example 20 MHz, 40 MHz, 80 MHz,160 MHz, etc. as described above but not limited to them. It is alsopossible to use three or more channels. It is considered here that thecombining of the channel M and the channel N may be regarded as onesingle channel.

It is assumed here that a terminal that implements OFDMA is capable ofcarrying out reception and decoding (including demodulation, decoding oferror correcting code, etc.) of a physical packet including a frame on achannel of at least the basic channel width (20 MHz channel width if anIEEE 802.11a/b/g/n/ac standard-compliant terminal is regarded as alegacy terminal) at the legacy terminal that is to be backwardcompatible. With regard to the carrier sense, it is carried out in aunit of the basic channel width. The carrier sense may encompass bothphysical carrier sense associated with busy/idle of CCA (Clear ChannelAssessment) and Virtual Carrier Sense based on medium reserve timedescribed in the received frame. As in the case of the latter, a schemefor virtually determining that a medium is in the busy state, or theterm during which the medium is virtually regarded as being in the busystate is called Network Allocation Vector (NAV). Here, carrier senseinformation based on CCA or NAV carried out in a unit of a channel maybe universally applied to all the resource units within the channel. Forexample, resource units belonging to the channel indicated as being inthe idle state by the carrier sense information are all in the idlestate.

With regard to OFDMA, channel-based OFDMA is also possible in additionto the above-described resource-unit-based OFDMA. OFDMA of this case mayin particular be called MU-MC (Multi-User Multi-Channel). In MU-MC, abase station assigns a plurality of channels (one channel width is, forexample, 20 MHz, etc.) to a plurality of terminals, and the plurality ofchannels are simultaneously used to carry out simultaneous transmissionsto the plurality of terminals or simultaneous receptions from theplurality of terminals. The OFDMA which will be described below meansthe resource-unit-based OFDMA: however, an embodiment of channel-basedOFDMA can also be implemented with appropriate replacement of terms andphrases in the following explanations such as reading the “resourceunit” as the “channel”.

Here, that in an uplink multiplex transmission from a plurality ofterminals to the base station, a communication scheme (which is calledOFDMA & MU-MIMO) that combines OFDMA and MU-MIMO (Multiple-InputMultiple-Output) is also possible in place of the above-described OFDMAscheme. In the uplink MU-MIMO transmission, streams are transmitted froma plurality of terminals by spatial multiplexing to the base station(simultaneously by the same frequency band), and the base stationsimultaneously receives these streams by a plurality of antennas. In thecase of OFDMA & MU-MIMO, a plurality of terminals use the same resourceunit and carry out MU-MIMO transmissions. When OFDMA is mentioned in thefollowing explanations, it may be read as OFDMA & MU-MIMO.

In the following explanations, a terminal having the capability ofcarrying out UL-OFDMA may be called an UL-OFDMA-compliant terminal (orsimply OFDMA-compliant terminal) or the like. A terminal that does nothave the capability may be called a legacy terminal. If the capabilityof carrying out UL-OFDMA communication can be selectively enabled ordisabled, a terminal whose capability of carrying out UL-OFDMAcommunication is enabled should be treated as the OFDMA-compliantterminal.

As illustrated in FIG. 1 , a wireless communication device incorporatedin a terminal (which may be either a terminal of non-base station or thebase station) includes a upper layer processor 90, a MAC processor 10, aphysical (PHY) processor 50, a MAC/PHY manager 60, an analog processor70 (analog processors 1 to N), and an antenna 80 (antennas 1 to N),where N represents an integer equal to or larger than 1. In the figure,the N analog processors and the N antennas are connected in pairs witheach other, but the configuration is not limited to the illustrated one.For example, one analog processor and two or more antennas may beconnected to this analog processor in a shared manner. The MAC processor10, the MAC/PHY manager 60, and the PHY processor 50 correspond to amode of controller, controlling circuitry or baseband integrated circuitthat carries out processing associated with communications with otherterminals (including the base station). The analog processor 70corresponds, for example, to a wireless communication unit or a radiofrequency (RF) integrated circuit that transmits and receives signalsvia the antenna 80. The integrated circuit for wireless communication inaccordance with this embodiment includes at least the former of thebaseband integrated circuit and the RF integrated circuit. The functionsof the communication processing device or the baseband integratedcircuit may be performed by software (programs) that runs on a processorsuch as a CPU or may be performed by hardware, or may be performed byboth of the software and the hardware. The software may be stored in astorage medium such as a memory device including a ROM, a RAM, etc., ahard disk, or an SSD and read therefrom to be executed. The memorydevice may be a volatile memory device such as an SRAM or a DRAM, or anon-volatile memory device such as a NAND or an MRAM.

The upper layer processor 90 is configured to carry out processing forthe Medium Access Control (MAC) layer associated with the upper layer orlayers. The upper layer processor 90 is capable of exchanging signalswith the MAC processor 10. As the upper layer, TCP/IP, UDP/IP, and theapplication layer upper than these two protocols may be mentioned astypical examples but this embodiment is not limited to them. The upperlayer processor 90 may include a buffer for exchanging data between theMAC layer and the upper layer or layers. It may also be considered thatit may be connectable to a wired infrastructure via the upper layerprocessor 90. The buffer may be a memory device, an SSD drive, or a harddisk. When the buffer is a memory device, the memory device may be avolatile memory device such as an SRAM or a DRAM, or a non-volatilememory device such as a NAND or an MRAM.

The MAC processor 10 is configured to carry out processing for the MAClayer. As described above, the MAC processor 10 is capable of exchangingsignals with the upper layer processor 90. Further, the MAC processor 10is capable of exchanging signals with the PHY processor 50. The MACprocessor 10 includes a MAC common processor 20, a transmissionprocessor 30, and a reception processor 40.

The MAC common processor 20 is configured to carry out common processingfor transmission and reception in the MAC layer. The MAC commonprocessor 20 is connected to and exchanges signals with the upper layerprocessor 90, the transmission processor 30, the reception processor 40,and the MAC/PHY manager 60.

The transmission processor 30 and the reception processor 40 areconnected to each other. Also, the transmission processor 30 and thereception processor 40 are each connected to the MAC common processor 20and the PHY processor 50. The transmission processor 30 is configured tocarry out transmission processing in the MAC layer. The receptionprocessor 40 is configured to carry out reception processing in the MAClayer.

The PHY processor 50 is configured to carry out processing for aphysical layer (PHY layer). As described above, the PHY processor 50 iscapable of exchanging signals with the MAC processor 10. The PHYprocessor 50 is connected via an analog processor 70 to an antenna 80.

The MAC/PHY manager 60 is connected to the upper layer processor 90, theMAC processor 10 (more specifically, the MAC common processor 20), andthe PHY processor 50. The MAC/PHY manager 60 is configured to manage MACoperation and PHY operation in the wireless communication device.

The analog processor 70 includes an analog-to-digital anddigital-to-analog (AD/DA) converter and a radio frequency (RF) circuit.The analog processor 70 is configured to convert a digital signal fromthe PHY processor 50 into an analog signal having a desired frequencyand transmit it from the antenna 80, or convert a high-frequency analogsignal received from the antenna 80 into a digital signal. It isconsidered here that although AD/DA conversion is carried out by theanalog processor 70, another configuration is also possible according towhich the PHY processor 50 has the AD/DA conversion function.

The wireless communication device in accordance with this embodiment hasits constituent element (i.e., incorporates) the antenna 80 in onesingle chip and thereby makes it possible to reduce the mounting area ofthe antenna 80. Further, in the wireless communication device inaccordance with this embodiment, as illustrated in FIG. 1 , thetransmission processor 30 and the reception processor 40 shares the Nantennas 80. By virtue of sharing the N antennas 80 by the transmissionprocessor 30 and the reception processor 40, it is made possible toreduce the size of the wireless communication device of FIG. 1 . It isconsidered here that the wireless communication device in accordancewith this embodiment may have a configuration different than the onedepicted by way of example in FIG. 1 .

In reception of a signal from a wireless medium, the analog processor 70converts an analog signal received by the antenna 80 into a basebandsignal that can be processed by the PHY processor 50, and furtherconverts the baseband signal into a digital signal. The PHY processor 50is configured to receive a digital signal that is received from theanalog processor 70 and detect its reception level. The detectedreception level is compared with the carrier sense level (threshold).When the reception level is equal to or larger than the carrier senselevel, the PHY processor 50 outputs a signal indicative of the fact thatthe medium (CCA: Clear Channel Assessment) is in the busy state to theMAC processor 10 (the reception processor 40 to be more precise). Whenthe reception level is less than the carrier sense level, the PHYprocessor 50 outputs a signal indicative of the fact that the medium(CCA) is in the idle state to the MAC processor 10 (the receptionprocessor 40 to be more precise).

The PHY processor 50 is configured to carry out decoding processing forthe received signal (including demodulation and decoding of errorcorrecting code, etc.), processing of removing a physical header (PHYheader) including a preamble, or the like, and extracts a payload.According to the IEEE 802.11 standard, this payload is called physicallayer convergence procedure (PLCP) service data unit (PSDU) on the PHYside. The PHY processor 50 delivers the extracted payload to thereception processor 40, and the reception processor 40 handles it as aMAC frame. According to the IEEE 802.11 standard, this MAC frame iscalled medium access control (MAC) protocol data unit (MPDU). Inaddition, the PHY processor 50, when it started to receive the receptionsignal, notifies the fact of having started reception of the receptionframe to the reception processor 40, and, when it completed thereception of the reception signal, notifies the fact of having completedthe reception to the reception processor 40. Also, the PHY processor 50,when the reception signal has been decoded successfully as the physicalpacket (PHY packet) (when it does not detect an error), notifies thecompletion of the reception of the reception signal and delivers asignal indicative of the fact that the medium is in the idle state tothe reception processor 40. The PHY processor 50, when it detected anerror in the reception signal, notifies the fact that the error has beendetected with an appropriate error code in accordance with the errortype to the reception processor 40. Also, the PHY processor 50, at thetiming at which the medium has been determined to enter the idle state,notifies a signal indicative of the fact that the medium is in the idlestate to the reception processor 40.

The MAC common processor 20 performs intermediary processing fordelivery of transmission data from the upper layer processor 90 to thetransmission processor 30 and for delivery of reception data from thereception processor 40 to the upper layer processor 90. According to theIEEE 802.11 standard, the data in this MAC data frame is called mediumaccess control (MAC) service data unit (MSDU). Also, the MAC commonprocessor 20 receives instructions from the MAC/PHY manager 60 and thenconverts the instruction into appropriate form of instructions for thetransmission processor 30 and the reception processor 40 and outputs theconverted instructions to these units.

The MAC/PHY manager 60 corresponds, for example, to station managemententity (SME) in the IEEE 802.11 standard. In that case, the interfacebetween the MAC/PHY manager 60 and the MAC common processor 20corresponds to MAC subLayer management entity service access point (MLMESAP) in the IEEE 802.11 standard, and the interface between the MAC/PHYmanager 60 and the PHY processor 50 corresponds to physical layermanagement entity service access point (PLME SAP) in the IEEE 802.11wireless local area network (LAN).

It is considered here that although the MAC/PHY manager 60 in FIG. 1 isillustrated on the assumption that the functional unit for the MACmanagement and the functional unit for the PHY management are configuredto be integral with each other, these units may be separatelyimplemented.

The MAC/PHY manager 60 stores Management Information Base (MIB). The MIBstores various pieces of information such as the capability of thedevice itself and whether various functions are enabled or disabled. Forexample, information may be stored regarding whether or not the deviceitself supports UL-OFDMA and, if the device itself supports UL-OFDMA,whether or not the function to implement UL-OFDMA is enabled ordisabled. A memory device for storing and managing the MIB may beincorporated in the MAC/PHY manager 60 or separately provided withoutbeing incorporated into the MAC/PHY manager 60. When the memory devicefor storing and managing the MIB is provided separately from the MAC/PHYmanager 60, the MAC/PHY manager 60 can refer to the separately providedmemory device and rewrite rewritable parameters within the memorydevice. The memory device may be a volatile memory device such as anSRAM or a DRAM, or a non-volatile memory device such as a NAND or anMRAM. Also, storage devices such as a hard disk and an SSD may be usedin place of the memory device. In the base station, these pieces ofinformation of the other terminals that are not a base station can alsobe obtained by notification from these terminals. In that case, theMAC/PHY manager 60 is adapted to be capable of referring to andrewriting the information regarding the other terminals. Alternatively,the memory device for storing the information on the other terminals maybe held and managed separately from the MIB. In that case, either theMAC/PHY manager 60 or the MAC common processor 20 is adapted to becapable of referring to and rewriting the separate memory device. Also,the MAC/PHY manager 60 of the base station may include a selectionfunction for, when implementing UL-OFDMA, selecting the terminals towhich the resource units for UL-OFDMA are assigned on the basis ofvarious pieces of information regarding terminals that are not a basestation, or on the basis of the requests from the terminals (i.e.,selecting the terminals subject to UL-OFDMA of this time). Also, theMAC/PHY manager 60 or the MAC processor 10 may manage the data(transmission) rate applied to the MAC frame and the physical headeraimed at transmission. Also, the MAC/PHY manager 60 of the base stationmay define and manage a supported rate set which is a rate set supportedby the base station. The supported rate set may include a rate thatshould compulsorily supported by the terminal that is connected to thebase station and an optional rate.

The MAC processor 10 is configured to handle three types of MAC frames,i.e., a data frame, a control frame, and a management frame, and carryout various processing procedures defined in the MAC layer. Here, thethree types of MAC frames are described.

The management frame is for use in management of communication link withanother terminal. As the management frame, for example, Beacon frame maybe mentioned. The Beacon frame notifies attribute and synchronizationinformation of a group to form a wireless communication group which is aBasic Service Set (BSS) in the IEEE 802.11 standard. Also, a frame forauthentication or establishing the communication link may also bementioned. It is considered here that a state where a certain terminalcompleted exchange of information necessary for establishing a wirelesscommunication with another terminal is expressed here as (the statewhere) the communication link is established. As the exchange ofnecessary information, for example, notification of the functions thatthe device itself supports (for example, support of the UL-OFDMA schemeand various capabilities which will be later described, etc.), andnegotiation regarding settings of the scheme may be mentioned. Themanagement frame is generated on the basis of the instruction receivedby the transmission processor 30 from the MAC/PHY manager 60 via the MACcommon processor 20.

With regard to the management frame, the transmission processor 30achieves notifying various pieces of information to other terminals bythe management frame. A terminal that is not a base station may notifythe type of the terminal itself to the base station by putting in themanagement frame information regarding such as whether it is anUL-OFDMA-compliant terminal, an IEEE 802.11n-compliant terminal, or anIEEE 802.11ac-compliant terminal. As for this management frame, forexample, Association Request frame used in the association process whichis one of the procedures for authentication between the terminal and thebase station or Reassociation Request frame used in the reassociationprocess may be mentioned. The base station may notify the information onwhether or not it supports UL-OFDMA communication to the terminal thatis not the base station by the management frame. As the management frameused for this, for example, Beacon frame and Probe Response frame may bementioned. The Probe Response frame is a response to the Probe Requestframe transmitted by the terminal that is not the base station. The basestation may have a function of grouping terminals which are connected toitself. The above-described notification means at the base station maynotify to each of the terminals a group ID by the management frame. Thegroup ID is a group identifier of the group to which the terminal itselfbelongs. As this management frame, for example, Group ID Managementframe may be mentioned. The group ID may be, for example, an identifierthat expands the concept of a group ID (six bits) defined for DL-MU-MIMOin the IEEE Std 802.11ac-2013 such that it covers a case of UL-OFDMA, ormay be a group ID that is defined in accordance with a method differentfrom this. Also, when designating this group and implementing UL-OFDMA,if there exists any necessary information for determining the resourceunits used by a terminal that belongs to this group, the base stationmay notify that information by a predetermined management frame (as willbe described later, when the group is designated, the terminal includesthe function of acquiring a resource unit based on a technique similarto random backoff procedure).

Here, association ID (AID) is described. The AID is an identifier(terminal identifier) of a terminal assigned by the base station to thisterminal in the association process for allowing the terminal to make aconnection to the base station and enabling data frame exchange in theBSS under the base station. The association process, specifically, is aprocess that is successful when an Association Request frame istransmitted from the terminal to the base station and an AssociationResponse frame is transmitted from the base station to the terminal andthe terminal Status Code field in the Association Response frame is “0”which represents the success. The communication capability of thetransmission terminal is included in both Association Request frame andAssociation Response frame, by virtue of which both parties thatreceived either of them grasp the communication capabilities of theircounterparts. When terminal Status Code field in the AssociationResponse frame is “0” representing the success, the AID is extractedfrom the AID field (16 bits) in the same frame and it is used as the AIDof the transmission destination terminal. In other words, the AID isassigned from the base station to the terminal at this point, and theterminal enters a state where the AID is enabled. In a state where thisbase station is connected to (have Association with) the terminal, theAID of the terminal is enabled. Meanwhile, when a Disassociation frameis transmitted from the base station to this terminal and this terminalreceives it, or when the Disassociation frame is transmitted from thisterminal to the base station, the AID of this terminal is disabled(null). It will be appreciated that the AID is null on a terminal thathas not had the association process with any base station. It can alsobe said that the state where the AID is null is a state where the AID isnot assigned.

The reception processor 40 has a receiver that receives various types ofinformation via the management frame from other terminals. As oneexample, the receiver of the base station may receive informationassociated with compatibility with UL-OFDMA communication from anyterminal as a non-base station. Also, it may receive informationassociated with an adaptable channel width (the maximum availablechannel width) if this terminal is a legacy terminal (IEEE802.11a/b/g/n/ac standard-compliant terminal and the like). The receiverof the terminal may receive from the base station information associatedwith compatibility as to whether or not UL-OFDMA is supported.

The examples of the information to be transmitted and received via themanagement frame as described above are merely examples and variousother types of information can be transmitted and received via themanagement frame between terminals (including the base station). Forexample, an UL-OFDMA-compliant terminal may select either or both of aresource unit and a channel that the terminal itself wants to use in theUL-OFDMA transmission from either or both of non-interference channelsand non-interference resources based on carrier sense. And informationregarding the resource unit, channel, or both of them that have beenselected may be notified to the base station. In this case, the basestation, on the basis of this information, may perform assignment of theresource units for the UL-OFDMA communication for each of theUL-OFDMA-compliant terminals. It is considered here that the channelsused in the UL-OFDMA communication may be all of the channels that areavailable as the wireless communication system or may be a subset (oneor a plurality) of the channels.

The data frame is for use in transmission of data to another terminal ina state where the communication link is established with the otherterminal. For example, data is generated in the terminal by an operationof an application by a user, and the data is carried by the data frame.Specifically, the generated data is delivered from the upper layerprocessor 90, via the MAC common processor 20, and to the transmissionprocessor 30, the data is put into the frame body field by thetransmission processor 30, and a MAC header is added to the this framebody field, and thus the data frame is generated. In addition, aphysical header is added to the data frame by the PHY processor 50, thephysical packet is generated, and the physical packet is transmitted viathe analog processor 70 and the antenna 80. Also, when the physicalpacket is received by the PHY processor 50, the PHY processor 50performs the processing for the physical layer on the basis of thephysical header, and extracts the MAC frame (here, the data frame), anddelivers the data frame to the reception processor 40. When thereception processor 40 receives the data frame (recognizes that thereceived MAC frame is a data frame), the reception processor 40 extractsthe information in the frame body field as data, and delivers theextracted data via the MAC common processor 20 to the upper layerprocessor 90. As a result, operations occur on applications such aswriting, reproduction, and the like of the data.

The control frame is for use in control in transmission and reception(exchange) of the management frame and the data frame to/from (with) theother wireless communication device. As the control frame, for example,RTS (Request to Send) frame, CTS (Clear to Send) frame may be mentionedwhich are exchanged with the other wireless communication device to makea reservation of the wireless medium prior to starting exchange of themanagement frame and the data frame. Also, as another control frame,delivery confirmation response frame for confirmation of delivery of thereceived management frame and the data frame may be mentioned. Asexamples of the delivery confirmation response frame, ACK(Acknowledgement) frame and BA (BlockACK) frame may be mentioned. Sincethe CTS frame is transmitted as a response to the RTS frame, it can besaid that the CTS is a frame that represents a delivery confirmationresponse. CF-End frame is also one of the control frames. The CF-Endframe is a frame that announces the completion of the CFP (ContentionFree Period) or the truncation of the TXOP after-mentioned, in otherwords, a frame permitting other wireless communication devices to accessthe wireless medium. These control frames are generated by thetransmission processor 30. With regard to the control frames (CTS frame,ACK frame, BA frame, etc.) transmitted as a response to the received MACframe, the reception processor 40 determines whether or not transmissionof a response frame (control frame) is necessary, and outputsinformation necessary for frame generation (type of the control frame,information specified in the RA (Receiver Address) field, and the like)to the transmission processor 30 along with the transmissioninstruction. The transmission processor 30 generates an appropriatecontrol frame on the basis of the information necessary for generationof the frame and the transmission instruction.

When a MAC frame is transmitted on the basis of CSMA/CA (Carrier SenseMultiple Access with Carrier Avoidance), the MAC processor 10 needs toacquire the access right (transmission right) on the wireless medium.The transmission processor 30, on the basis of carrier sense informationfrom the reception processor 40, measures the transmission timing. Thetransmission processor 30, in accordance with the transmission timing,gives the transmission instruction to the PHY processor 50, and furtherdelivers the MAC frame thereto. In addition to the transmissioninstruction, the transmission processor 30 may instruct a modulationmethod and a coding method to be used in the transmission. In additionto them, the transmission processor 30 may provide an instructionregarding the transmission power. When the MAC processor 10, afterhaving acquired the access right (transmission right), obtained theperiod of time during which the medium can be occupied (TransmissionOpportunity; TXOP), then the MAC processor 10 is allowed to continuouslyexchange the MAC frames with other wireless communication devicesalthough there is some limitation such as the QoS (Quality of Service)attribute. The TXOP is acquired, for example, when the wirelesscommunication device transmits a predetermined frame (for example, anRTS frame) on the basis of CSMA/CA (Carrier Sense Multiple Access withCarrier Avoidance) and correctively receives a response frame (forexample, a CTS frame) from another wireless communication device. Whenthis predetermined frame is received by the other wireless communicationdevice, the other wireless communication device transmits the aboveresponse frame after the elapse of the minimum frame interval (ShortInterFrame Space; SIFS). Also, as a method of acquiring the TXOP withoutusing the RTS frame, for example, cases may be mentioned where dataframe that requests transmission of the delivery confirmation responseframe is transmitted directly by the unicast (as will be describedlater, this frame may be a frame in the form of conjunct frames orconjunct payloads) or a management frame that requests transmission ofthe delivery confirmation response frame is transmitted, and deliveryconfirmation response frame (ACK frame, BlockACK frame or the like) inresponse thereto is correctly received. Alternatively, when a frame istransmitted that does not request, for the other wireless communicationdevice, transmission of the delivery confirmation response frame with aperiod equal to or longer than the time period needed to transmit thisframe specified in the Duration/ID field of this frame, then it may beinterpreted that with the transmission of this frame, TXOP of the perioddescribed in the Duration/ID field has been acquired.

The reception processor 40 is configured to manage the above-describedcarrier sense information. This carrier sense information includes bothPhysical Carrier Sense information regarding busy/idle states of themedium (CCA) input from the PHY processor 50 and Virtual Carrier Senseinformation on the basis of the medium reserve time described in thereceived frame. If either one of these carrier sense information piecesindicates the busy state, then the medium is regarded as being in thebusy state in which transmission is prohibited. It is considered herethat in the IEEE 802.11 standard, the medium reserve time is describedin the Duration/ID field in the MAC header. The MAC processor 10, whenhaving received a MAC frame that is addressed to other wirelesscommunication devices (that is not addressed to the device itself),determines that the medium is virtually in the busy state from the endof the physical packet including this MAC frame over the medium reservetime. A scheme of this type for virtually determining that a medium isin the busy state, or the term during which the medium is virtuallyregarded as being in the busy state is called Network Allocation Vector(NAV). It can be said that the medium reserve time represents the lengthof time period during which suppression of accesses to the wirelessmedium is instructed, i.e., the length of time period during whichaccesses to the wireless medium are deferred.

Here, the MPDU may be a frame such that a plurality of MAC frames areconjunct with each other or payload portions of a plurality of MACframes are conjunct with each other. The former data frame is called A(Aggregated)-MPDU and the latter data frame is called A(Aggregated)-MSDU (MAC service data unit) in the IEEE 802.11 standard.In the case of the A-MPDU, a plurality of MPDUs are conjunct with eachother within the PSDU. Also, as a MAC frame, in addition to the dataframe, the management frame and the control frame are also eligible forthis conjunction. In the case of the A-MSDU, MSDUs which are a pluralityof data payloads are conjunct with each other within the frame body ofone MPDU. In both cases of the A-MPDU and the A-MSDU, partitioninformation (length information, etc.) is stored in the frame such thatthe conjunction of the MPDUs and combination of MPDUs can beappropriately separated by the terminal on the reception side. Both ofthe A-MPDU and the A-MSDU may be used in combination. Also, the A-MPDUmay involve not a plurality of MAC frames but one single MAC frame, andalso in this case the partition information is stored in the frame.Also, when an A-MPDU or the like is received, responses to the pluralityof MAC frames being conjunct are transmitted together. The BA (BlockACK)frame is used as the response in this case in place of the ACK frame. Inthe following explanations and figures, the notation of MPDU may beused, but it is assumed here that this notation includes the cases ofthe above-described A-MPDU and the A-MSDU.

According to the IEEE 802.11 standard, several procedures are defined inmultiple stages to be taken for a terminal that is not the base stationto participate in a BSS (which is called Infrastructure BSS) configuredwith the base station amongst others and to perform exchange of dataframes within the BSS. For example, there is provided a procedure calledassociation, according to which an Association Request frame istransmitted from the terminal that is not the base station to the basestation to which the terminal requests the connection. The base station,after having transmitted an ACK frame for the association request frame,transmits an Association Response frame which is a response to theassociation request frame.

The terminal stores the capability of the terminal itself in theassociation request frame and transmits this association request frame,and thus can make notification of the capability of the terminal itselfto the base station. For example, the terminal may add, to theassociation request frame, the channel, the resource unit, or both ofthem that the terminal itself can support, and information foridentifying the standard supported by the terminal itself into theassociation request frame and transmit this association request frame.This information may be also set in the frame transmitted by theprocedure called reassociation (reassociation) to reconnect to anotherbase station. In this procedure of reassociation, a ReassociationRequest frame is transmitted to the other base station to whichreconnection is requested from the terminal. The other base station,after having transmitted the ACK frame in response to the reassociationrequest frame, transmits a reassociation response which is a response tothe reassociation request frame.

As the management frame, in addition to the association request frameand the reassociation request frame, a beacon frame, a probe responseframe, etc. may be used. The beacon frame is basically transmitted bythe base station, and is capable of storing parameter notifying thecapability of the base station itself along with the parametersindicating the attributes of the BSS. In view of this, as the parameternotifying the capability of the base station itself, the base stationmay be adapted to add the information on whether or not UL-OFDMA issupported. Also, as the other parameter, information on the supportedrates of base station may be notified. The supported rates may includemandatory rates required to be supported by the terminals participatingin the BSS formed by the base station and an optional rate. The proberesponse frame is a frame transmitted from the terminal that transmitsthe beacon frame in response to a probe request frame received. Theprobe response frame is basically the one that notifies the same contentas that of the beacon frame, and the base station, when it uses theprobe response frame, is also capable of notifying the capability of thestation itself to the terminal that transmitted the probe request frame.By making this notification to the UL-OFDMA-compliant terminal, anoperation may be performed according to which the terminal, for example,enables the function of the UL-OFDMA communication of the terminalitself.

It is considered here that the terminal may notify the informationregarding the rates available on the device itself from among thesupported rates of the base station rate as the information fornotifying the capability of the device itself to the base station.Meanwhile, it is considered that with regard to the mandatory rates fromamong the supported rates, a terminal that is connected to the basestation has the capability of executing the mandatory rates.

It is considered here that if notification of some piece or pieces ofinformation among the pieces of information mentioned above leads todefinition of the content of another piece or other pieces ofinformation, then notification of the other piece or pieces ofinformation may be omitted. For example, suppose a case where a terminalis always an UL-OFDMA-compliant terminal if a capability that iscompliant with a new standard or specifications is defined and as longas the terminal is compliant with that capability or specifications. Inthis case, as the above certain piece or pieces of information, presenceof the capability to be compliant with the standard or specification isnotified, and as the other piece or pieces of information, notificationof the fact that the terminal is an OFDMA-compliant terminal does notneed to be explicitly performed.

FIG. 4 illustrates a wireless communication system in accordance withthis embodiment. This system includes the base station (AP: AccessPoint) 100 and a plurality of terminals (STA: STAtion) 1 to 8. The BSS(Basic Service Set) 1 is formed by the base station 100 and theterminals 1 to 8 operating under the base station 100. This system is awireless LAN system compliant with the IEEE 802.11 standard usingCSMA/CA (Carrier Sense Multiple Access with Carrier Avoidance). It isconsidered here that legacy terminals (IEEE 802.11a/b/g/n/acstandard-compliant terminals, etc.) other than the terminals (UL-OFDMAterminals) in accordance with this embodiment may exist within the BSS1.

FIG. 5(A) illustrates the basic exemplary format of the MAC frame. Thedata frame, the management frame, and the control frame in accordancewith this embodiment are based on a frame format of this type. Thisframe format includes the fields of MAC header, Frame body, and FCS. TheMAC header includes, as illustrated in FIG. 5(B), the fields of FrameControl, Duration/ID, Address 1, Address 2, Address 3, Sequence Control,QoS Control, and HT (High Throughput) Control.

These fields do not need to always exist and there may be cases wheresome of these fields do not exist. For example, there may be a casewhere the Address 3 field does not exist. Also, there may be other caseswhere both or either one of the QoS Control field and the HT Controlfield does not exist. Also, there may be still other cases where theframe body field does not exist. Also, any field or fields that are notillustrated in FIG. 5 may exist. For example, an Address 4 field mayfurther exist. Also, an RU/AID field which will be described later mayexist in the MAC header or the frame body field.

The field of Address 1 indicates Receiver Address (RA), the field ofAddress 2 indicates Transmitter Address (TA), and the field of Address 3indicates either BSSID (Basic Service Set IDentifier) (which may be thewildcard BSSID whose bits are all set to 1 to cover all of the BSSIDsdepending on the cases) which is the identifier of the BSS, or TA,depending on the purpose of the frame. Meanwhile, as will be describedlater, one of the features of this embodiment is that the Address 1 andAddress 2 fields are to be used in a manner different than the one thathas been described here.

As described above, two fields of Type and Subtype (Subtype) or the likeare set in the Frame Control field. The rough classification as towhether it is the data frame, the management frame, or the control frameis made by the Type field, and more specific types, for example, finediscrimination among the roughly classified frames, for example, as towhether it is a BA frame or a BAR frame within the control frame, or abeacon frame within the management frame is made by the Subtype field.The trigger frame which will be described later may also bediscriminated by the combination of the Type and the Subtype. It islikely that the trigger frame is categorized as the control frame.

The Duration/ID field describes the medium reserve time, and it isdetermined that the medium is virtually in the busy state from the endof the physical packet including this MAC frame to the medium reservetime when a MAC frame addressed to another terminal is received. Thescheme of this type to virtually determine that the medium is in thebusy state, or the period during which the medium is virtually regardedas being in the busy state, is, as described above, called NAV (NetworkAllocation Vector). The QoS field is used to carry out QoS control tocarry out transmission with the priorities of the frames taken intoaccount.

In the management frame, an information element (Information element;IE) to which a unique Element ID (IDentifier) is assigned is set in theFrame Body field. One or a plurality of information elements may be setin the frame body field. The information element has, as illustrated inFIG. 6 , the fields of an Element ID field, a Length field, and anInformation field. The information element is discriminated by theElement ID. The Information field is adapted to store the content of theinformation to be notified, and the Length field is adapted to store thelength information of the information field.

Frame check sequence (FCS) information is set in the FCS field as achecksum code for use in error detection of the frame on the receptionside. As an example of the FCS information, CRC (Cyclic Redundancy Code)may be mentioned.

FIG. 7 illustrates an exemplary operation sequence of the base station(AP) 101 and a plurality of terminals including the terminals (STAs) 1to 8 in accordance with this embodiment. The terminals 1 to 8 areUL-OFDMA-compliant terminals.

In this exemplary operation sequence, as its premise, CSMA/CA-basedcommunications are individually carried out (single user communications)between the base station and all or part of the terminals 1 to 8. In thesingle user communications, communications are carried out between thebase station and the terminals, for example, on one channel with thebasic channel width (for example, 20 MHz). As one example of the singleuser communications, when data for uplink transmission is held by theterminal, the right to access the wireless medium is acquired inaccordance with CSMA/CA. As a result, the terminal carries out carriersense for the carrier sense time (waiting time) between theDIFS/AIFS[AC] and a randomly defined back-off time, and when it has beendetermined that the medium (CCA) is in the idle state, the terminalacquires the right to access to transmit, for example, one frame. Theterminal transmits the data frame (more specifically, a physical packetincluding the data frame). When the base station has received this dataframe successfully, then the base station returns an ACK frame (morespecifically, a physical packet including the ACK frame) which is adelivery confirmation response frame after the elapse of SIFS time aftercompletion of reception of the data frame. The terminal upon receptionof the ACK frame determines that the transmission of the data frame hasbeen successful. It is considered here that the data frame to betransmitted to the base station may be an aggregation frame (A-MPDU,etc.), and the delivery confirmation response frame by which the basestation respond may be a BA frame (this also applies to the followingexplanations). It is considered here that the DIFS/AIFS [AC] time refersto either the DIFS time or the AIFS [AC] time. When it is notQoS-compliant, the DIFS/AIFS [AC] time refers to the DIFS time. When itis QoS-compliant, the DIFS/AIFS [AC] time refers to the AIFS [AC] timewhich is defined in accordance with the access category (AC) (to belater described) of the data to be transmitted.

The base station decides to start UL-OFDMA at a predetermined timing.This example contemplates a case where UL-OFDMA transmission isperformed by the same channel as that of the single user communication(one channel with the basic channel width of 20 MHz). In other words, itis considered in this example that the UL-OFDMA transmission isperformed using a plurality of resource units defined within the channelwith the basic channel width of 20 MHz. Nevertheless, it is alsopossible to use other channel widths such as 40 MHz, 80 MHz, etc. toperform the UL-OFDMA transmission.

When the base station decides to start the UL-OFDMA transmission, thebase station transmits the trigger frame 501 of the UL-OFDMAtransmission (more specifically, a physical packet including the triggerframe). The trigger frame 501 is transmitted by the same channel as thatof the single user communication which is the channel with the basicchannel width. The physical packet including the trigger frame is, asone example, a packet in which a physical header is added to thebeginning of the trigger frame. The physical header is, as one example,as illustrated in FIG. 8 , includes L-STF (Legacy-Short Training Field),L-LTF (Legacy-Long Training Field), and L-SIG (Legacy Signal Field)defined in the IEEE 802.11 standard. The L-STF, L-LTF, and L-SIG fieldsare fields that can be recognized by terminals compliant with legacystandards, for example, such as IEEE 802.11a, in which pieces ofinformation are stored such as signal detection, frequency correction(propagation path estimation), and data rate, respectively. Fields otherthan those mentioned herein (for example, fields that terminalscompliant with legacy standards cannot recognize but UL-OFDMA-compliantterminals can recognize) may be included.

The trigger frame 501 may be a frame that can be received and decoded bylegacy terminals as well as the UL-OFDMA-compliant terminals. It isconsidered here that when the base station attempts to transmit thetrigger frame, the base station acquired the access right in accordancewith CSMA/CA in advance. Acquisition of the access right proceeds in thesame or similar manner as in the terminals described above. There are aplurality of frame formats and usage rules (rules of interpretation) forthe trigger frame 501 in this embodiment, and the operations of theterminal also vary depending on either one of them at the time ofreceiving the trigger frame 501. In the explanation of this sequence, atypical example of the operation is described and variant operationswill be later described. It is assumed here that the trigger frame 501includes, as one example, information identifying the plurality ofresource units that can be used in the UL-OFDMA transmission andinformation identifying a plurality of terminals that become candidatesfor the UL-OFDMA transmission. The above information identifying theresource units identifies, for example, all or part of the plurality ofresource units defined within the channel. The above informationidentifying the plurality of terminals that become the candidatesincludes, for example, at least one group ID or individual identifiersof the plurality of terminals (AID or MAC address, etc.). Examples otherthan those mentioned herein can also be considered.

The trigger frame 501 transmitted from the base station is received bythe terminals 1 to 8. The terminals 1 to 8 decodes the trigger frame501, and determines whether or not the terminal itself belongs to thegroup having the group ID designated by the trigger frame 501. It isconsidered here that the terminal is notified from the base stationabout the group ID of the group to which the terminal itself belongs, atthe time of the association process or at a predetermined timing afterthe association process. It may receive notification of thecorrespondence between the terminals other than the terminal itself andthe groups. When the terminal itself belongs to the group having thegroup ID designated by the trigger frame and the terminal itself holdsthe data for uplink transmission, then the terminal itself randomlyacquires a resource unit or units to be used by the terminal itself fromamong resource units designated by the trigger frame 501 based on atechnique similar to random backoff procedure. A terminal that does nothold the data for the uplink transmission does not need to make thisacquisition, but may be adapted to make the same acquisition. The numberof resource units to be acquired may be given in advance or may bedesignated by the trigger frame 501, or may be recognized by any othermethods. It is considered here that each of the terminals belonging tothe above-described group can acquire one resource unit at most.

It is assumed here that n resource units 1 to n are designated in thetrigger frame 501 as the information identifying the resource units. Theresource units 1 to n may be all of the resource units defined withinthe channel used in UL-OFDMA or may be part of these resource units. Theresource units 1 to n may, for example, be discriminated by RU #1 to RU#n which are their individual identifiers or numbers. Anotherconfiguration may also be considered in which an identifier thatidentifies a set of resource units is independently defined and one ormore identifiers of the sets are designated by the trigger frame 501. Inthis case, terminal recognizes the available resource units by theidentifier of the set.

In this example, it is assumed that a group to which the terminals 1, 3,4, and 6 commonly belong is designated from among the terminals 1 to 8and the group to which at least one of the terminals 2, 5, 7, and 8belongs was not designated. As one example, it is assumed that a groupincluding the terminals 1, 3, 4, and 6 and a group including theterminals 2, 5, 7, and 8 are defined by the base station, and only thegroup ID of the former group has been designated. And it is assumed thatthe terminals 1, 3, 4, and 6 individually holds the data for uplink, allof these terminals acquired the right to select the resource units, andthe resource units 2, 4, 6, and 7 have been randomly selected from amongthe resource units 1 to n. The terminals 1, 3, 4, and 6 transmit to thebase station the data frames 511, 513, 514, and 516 (more specifically,the physical packets including these data frames) including data foruplink transmission after the elapse of a predetermined time period T1after completion of the reception of the trigger frame 507. Thetransmission of the data frames 511, 513, 514, and 516 is performedusing the resource units 2, 4, 6, and 7 selected by the terminals 1 to4, respectively.

The predetermined time period T1 is, as one example, an SIFS (ShortInter-frame Space) time (=16 μs) which is a time interval between framesdefined in the MAC protocol specification of the IEEE 802.11 wirelessLAN, or other time intervals (IFS) defined in advance may be used. Thepredetermined time period T1 may be defined by the system or thespecification, or may be notified in advance by another method such asthe beacon frame or any other management frames. As another example, thevalue of the predetermined time period T1 may be stored in apredetermined field of the trigger frame 501 and the terminals 1 to 4may acquire the value of the predetermined time period T1 from thepredetermined field.

The transmission timings of the data frames transmitted by the terminals1, 3, 4, and 6 are synchronized with each other, and thus the UL-OFDMAtransmission is executed. It is considered here that when the terminalmakes an operation to select the resource unit though there is no datato be uplink-transmitted, then this terminal may transmit a Null Packetwhich is a frame having a predetermined format, for example, a framethat includes physical and MAC headers but does not include a datafield. Alternatively, this terminal may be adapted to select theresource unit but does not perform any transmission operation. The basestation, when having received the Null Packet, may determine that thisterminal did not have any data to be transmitted.

The base station receives the data frames 511, 513, 514, and 516 (morespecifically, the physical packets including the data frames)transmitted in accordance with OFDMA from the terminals 1, 3, 4, and 6.The base station receives the data frames 511, 513, 514, and 516 by theresource units 2, 4, 6, and 7, respectively. Since transmission of dataframes is not performed from any terminals in the other resource units,the base station does not perform the reception of the data frame inother resource units, either.

When the base station correctly receives the data frames transmittedfrom the terminals 1, 3, 4, and 6, the base station transmits thedelivery confirmation response frames 521 to the terminals 1, 3, 4, and6 after the elapse of a predetermined time period T2 after reception ofeach data frame. The predetermined time period T2 is, as one example, anSIFS (Short Inter-frame Space) time (=16 μs) which is a time intervalbetween frames defined in the MAC protocol specification of the IEEE802.11 wireless LAN, or other time intervals (IFS) defined in advancemay be used.

As the transmission of the delivery confirmation response frame 513, theBA frame is transmitted by the resource unit by which respective dataframe was received for each of the terminals 1, 3, 4, and 6. When thedata frame transmitted to the base station includes not an A-MPDU but aconventional (single) MPDU, an ACK frame may also be used in place ofthe BA frame (it is considered here that it is possible to return a BAframe in the case of conventional MPDU). In this manner, transmission ofthe BA (or ACK) frames by respective resource units for each of theterminals 1, 3, 4, and 6 corresponds to transmission of the deliveryconfirmation response frames by downlink OFDMA. In this case, eachterminal receives the BA (or ACK) frame by its own resource unit(reception filters are set such that the signals can be received in thismanner in units of the resource units). As another method, BA frames (orACK frames) can be transmitted to the terminals 1, 3, 4, and 6 bydownlink MU-MIMO. The downlink MU-MIMO is defined by the IEEE 802.11acstandard.

Further, as another method, a single frame that includes all of thedelivery confirmation responses for the terminals 1, 3, 4, and 6 may betransmitted with the channel width band (single user transmission). Inthis case, this frame may be called a Multi-STA BA frame. As a specificconfiguration, for example, Multi-TID BA frame defined by the IEEE802.11 standard may be diverted. As one example, the BA informationfields of the Multi-TID BA frame are arranged in the number equal to thenumber of the terminals and the identifier of the terminal (for example,AID (Association ID) or part of the AID) is set in the reserve field inthe TID information subfield of each BA information field. Values of theBlock Ack Starting Sequence Control subfield and Block Ack Bitmapsubfield of the of each BA information field should be set in aconventional manner in accordance with the data frames 511, 513, 514,and 516 to which the delivery confirmation responses should be returned.A multicast address of the group to which all of the terminals 1, 3, 4,and 6 belong or the broadcast address should be set in the RA (receiveraddress) of the Multi-STA BA frame. By this setting, the BA can benotified to a plurality of terminals by one single frame. Also, as theSubtype of the Frame Control field, a new value may be defined.

When ACK frames are returned to the terminals 1, 3, 4, and 6 instead ofBA frames, identifiers of the terminals are set in some fields of thereserve fields within the TID information subfield of each BAinformation field, and a part of the remaining fields of the reservefields are enabled (set to 1(s)). In addition, when this bit is or thesebits are enabled, the Block Ack Starting Sequence Control subfield andthe Block Ack Bitmap subfield are omitted (do not exist). By virtue ofthis, ACKs of the plurality of terminals can be notified to theterminals by one single frame. The other example will be to use thepartial state operation to cover the corresponding sequence number inthe Block Ack Bitmap subfield. The examples described herein are merelyexamples and existing frames other than the Multi-TID BA frame may bediverted, or a new frame may be defined without diverting the existingframes.

Although the above explanation illustrates an example where the deliveryconfirmation response frames 521 are transmitted at one time to theterminals 1, 3, 4, and 6, a method is also possible that returns BAframes or the ACK frames in a sequential manner to terminals 1, 3, 4,and 6 one by one. For example, it is also possible that, when the BAframes are returned in a sequential manner, a BA frame is returned to apredetermined terminal (for example, the terminal 1) after the elapse ofSIFS time after completion of the reception of the data frame, BARframes are received from the remaining terminals one by one and, asresponses thereto, BA frames are transmitted. Alternatively, with regardto the remaining terminals, BA frames may be transmitted from the basestation without reception of the BAR frames and in response thereto theACK frame may be received at the base station. It is also possible thatthe BA frames or ACK frames are returned in accordance with methodsother than the one described herein.

After transmission of the delivery confirmation response frame 521 bythe base station, the same or similar sequence starting the transmissionof the trigger frame from the base station may be repeatedly performed.

In the above-described exemplary operation, the terminal that isdesignated by the group ID by the trigger frame and having a right toselect a resource unit randomly selects the resource unit from among theplurality of resource units designated by the trigger frame. As anotheroperation, an operation is also possible according to which the basestation individually designates by the trigger frame the resource unitson a per-terminal basis, and the terminal designated by the triggerframe selects the resource unit designated by the trigger frame. Forexample, the identifiers (AIDs, etc.) of the terminals 1, 3, 4, and 6are designated by the trigger frame, and the identifiers of the resourceunits 2, 4, 6, 7 are individually designated for each of theseterminals. By virtue of this, a sequence that is the same or similar tothat of FIG. 7 is performed. It may also be considered that severalconsecutive resource units are assigned to the same terminal. Also, anoperation that combines both of these operations (random selection andindividual designation of the resource units) is also possible. Also, itmay be further considered that the resource units are designated, by thetrigger frame, for terminals that are yet to be connected to the basestation by including these terminals as being eligible for the UL-OFDMA.The following explains in more detail the exemplary configuration andusage (exemplary interpretation) of the trigger frame 501 and theoperations of the base station and the terminals in accordance with theexemplary configuration for realizing these operations.

FIG. 9(A) illustrates an exemplary configuration of the trigger frame501. An RU/AID field is added to the MAC header of the MAC frameillustrated in FIG. 5 whilst some of the fields such as the Address 3field, etc. are deleted. Nevertheless, all or part of these deletedfields may exist in the frame configuration of FIG. 7 . FIG. 9(B) is anexample of the case where the RU/AID field exists not in the MAC headerbut in the frame body field. When the RU/AID field is provided in theframe body field and if the trigger frame 501 is a management frame,then, as illustrated in FIG. 6 , as the information element, it may beconsidered to provide the RU/AID field. If the frame is a control frameor a data frame, then the RU/AID field should be added to the frame bodyfield in a form that allows the field to be identified. In the followingexplanations, unless there is the need of particular distinction,whether the RU/AID field exists in the MAC header or the frame bodyfield does not affect the applicability of the explanations.

FIG. 10 illustrates an exemplary configuration of the RU/AID field ofthe trigger frame and examples of the field lengths. The field lengthsillustrated herein are merely examples and other values may be used. Forexample, the field lengths are illustrated here in units of octets (8bits), but such an illustration in units of octets is not essential. Thesymbol “3×n” represents 3 multiplied by n.

The RU/AID field includes n pairs of an RU field (RU_1 to RU_n) and anAID field (AID_1 to AID_n). As basic usage of this frame format,designation of the resource units and designation of the terminals towhich the resource units are assigned are carried out using the RU fieldand the AID field. The identifier of the resource unit is specified bythe RU field, and the identifier (here, the AID) of the terminal towhich the resource unit is assigned is specified by the AID field. Byvirtue of this, the terminals are designated for each of the resourceunits and each of the terminals uses the designated resource unit. Here,the Type of the frame control field is set as “Control” or “Management”whilst a new value is defined for the Subtype in accordance with thetrigger frame. The Type does not need to be “Control” or “Management”but may be set as “Data.” In this case, it may be considered that afield notifying whether or not it is a trigger frame is separatelyprovided in the MAC header in place of defining a new value for theSubtype, the bit is set in this field, and thereby notification of thefact that it is the trigger frame is performed. In the Duration/IDfield, the length of the period is designated during which exclusive useof the wireless medium should be allowed from the end of the triggerframe. For example, a length of time until the end of the deliveryconfirmation response frame is designated. Values of the SequenceControl field and the FCS field should be set in a conventional manner.In the Address 1 field, a broadcast address or a multicast addressshould be set as an RA. Address 2 field, the MAC address (BSSID) of thebase station should be set as TA. It is considered here that the value n(the number of pairs of the RU field and the AID field) may be a fixedvalue or a variable value. When it is a variable value, then a fielddefining the value n may be provided at the beginning of the RU/AIDfield, or a field notifying the end of the RU/AID field may be provided.The field notifying the end may be a special value that is not found inthe combination of the identifier of the resource unit and the AID.

In the following, examples are illustrated where the frame formatshaving the configuration of the RU/AID field of this type are used, theterminal group is designated by the group ID as illustrated in FIG. 7 ,and resource units are acquired by the terminals belonging to this groupID based on a technique similar to random backoff procedure to performthe frame transmission.

First Example

In this case as well, identifiers of the available resource units areset in the RU fields (RU_1 to RU_n). In the example of FIG. 10 , thereexist n RU fields, and identifiers of the corresponding resource unitsare set in these RU fields. Meanwhile, predetermined values are set inthe n AID fields (AID_1 to AID_n) in the first example.

Meanwhile, the Type of the frame control field is set as “Control” or“Management,” and a new value is defined for the Subtype in accordancewith the trigger frame. Type does not need to be “Control” or“Management” but may be set as “Data.” In this case, it may beconsidered that a field notifying whether or not it is a trigger frameis separately provided in the MAC header in place of defining a newvalue for the Subtype, and the bit is set in this field, and therebynotification of the fact that it is the trigger frame is performed. Inthe Duration/ID field, the length of the period is designated duringwhich exclusive use of the wireless medium should be allowed from theend of the trigger frame. For example, a length of time until the end ofthe delivery confirmation response frame is designated. Values of theSequence Control field and the FCS field should be set in a conventionalmanner.

The group ID of the group to which candidate terminals (terminals 1, 3,4, and 6 in the example of FIG. 7 ) belong is set in the Address 1field. Since, in normal cases, an RA (unicast address, broadcastaddress, or multicast address) is set in the Address 1 field, it is anoperation different than the normal operation to set a group ID thereto.As a result, it is necessary to notify the fact that the group ID is setin the Address 1 field. In view of this, the MAC address (BSSID) of thebase station with the Individual/Group bit (bit of a particularlocation) converted into 1 is set in the Address 2 field. Since a TA isset in the Address 2 field in normal cases, a normal operation is to setthe MAC address (BSSID) of the base station. Here, in order to notifythe fact that a group ID is set in the Address 1 field, the MAC address(BSSID) of the base station with the Individual/Group bit converted into1 is set therein. The Individual/Group bit is the eighth bit of the MACaddress (when the MAC address is transferred, it is transmitted in unitsof octets from its beginning, and the least significant bit istransmitted first among the bits in one octet, so that theIndividual/Group bit is the first bit in transfer of the MAC address),and the value of the Individual/Group bit for the MAC address of aterminal (including a base station) is 0. It is considered here that thevalue is 1 in the case of the broadcast address or multicast address. Inview of this, the fact that a group ID is set in the Address 1 field isnotified to the terminal by converting this Individual/Group bit from 0to 1 (since in normal cases the trigger frame is transmitted from thebase station, the TA to be set in the Address 2 field is the MAC addressof the base station and the fact is relied on that the Individual/Groupbit is 0). Hence, since Individual/Group bit of the Address 2 field is1, the terminal is allowed to determine that the group ID is set in theAddress 1 field and determine that the transmitter address of thetrigger frame takes a value equal to the Individual/Group bit of the bitsequence of the Address 2 field whose 1 is cleared to 0. Accordingly, asthe RA at the time of transmission of the data frame by the terminal, itis possible to use the bit sequence of the Address 2 field with theIndividual/Group bit cleared to 0 (i.e., the MAC address of the basestation).

It is considered here that the value n (the number of pairs of the RUfield and the AID field) may be a fixed value or a variable value. Whenit is a variable value, then a field defining the value n may beprovided at the beginning of the RU/AID field, or a field notifying theend of the RU/AID field may be provided. The field notifying the end maybe a special value that is not found in the combination of theidentifier of the resource unit and the AID.

The terminal that has received the trigger frame specified in theabove-described manner recognizes the fact that the trigger frame hasbeen received, for example, from the values of the Type and the Subtypeof the frame control field. Since the Individual/Group of the Address 2field is set to 1, it recognizes the fact that the group ID is set inthe Address 1 field and reads the group ID set in the. Address 1 field.It is determined whether or not the terminal itself belongs to the groupindicated by the group ID. If the terminal itself does not belong to thegroup, the trigger frame is discarded and the process is terminated. Ifthe terminal itself belongs to the group indicated by the group ID, theRU/AID field is checked. And the resource units indicated by theidentifiers set in the n RU fields are recognized as the availableresource unit candidates. The n AID fields are ignored. The terminal,for example, subtracts the number of the available resource unitcandidates from a backoff counter which was randomly selected and if theresult is equal to or less than zero, it randomly selects the resourceunit to be used by the terminal itself from among the available resourceunit candidates. It is considered here that one single resource unit isto be selected, but, as described above, a plurality of resource unitsmay be selected. Any methodology can be relied on for the randomselection. For example, a random number generator that generatesnumerical value with a predetermined number of digits may be used toidentify the resource unit having the number obtained by dividing therandom number by n and adding 1 to the remainder. In this case, when thevalue of the remainder is zero, then the resource unit 1 is selected. Ifthe value of the remainder is n−1, then the resource unit n is selected.The example described herein is merely an example and it will beappreciated that other methods may be used. The terminal uses therandomly selected resource unit and transmits the data frame asdescribed above. It is considered here that the RA (the value of theAddress 1 field) of the data frame is the MAC address (BSSID) of thebase station, and the TA (the value of the Address 2 field) is the MACaddress of the terminal itself.

In accordance with the above-described first example, since only theterminals that belong to the group designated by the group ID become theUL-OFDMA candidate terminals, it is made possible to reduce thelikelihood of overlapping of the randomly selected resource unitsbetween terminals more significantly than a case where all of theterminals that have received the trigger frames become the candidateterminals. It is considered here that when the same resource unit isselected by a plurality of terminals, signal interference occurs withinthe resource unit at the base station, which leads to failure inreceiving the frames from these terminals.

Second Example

The second example differs from the first example in the setting of then AID fields and in the operation of the terminal. The difference withrespect to the first example is explained below. Unused values that arenot used as an AID, or AIDs assigned to the terminal are set in the nAID fields. The “unused value that is not used as an AID” refers to avalue that is out of the range of the AID values that the base stationcan assign. For example, when the base station uses fourteen bits out ofthe two octets (16 bits) to represent the AID, if the range of thevalues that the base station can assign is not less than 1 and notlarger than 2007, then the fourteen bits from the two octets (16 bits)of the AID field (the zeroth to thirteenth bits) are all cleared to 0 orset to a value within the range from 2008 to 16383. Fixed values are setto the fourteenth and fifteenth bits (for example, “11”). It isconsidered here that the exemplary setting of the unused value of theAID as described herein is similar to the method defined in the IEEE802.11 standard which uses the reserved area of the Duration/ID field(see IEEE Std 802.11™-2012, Table 8-3). When the terminals are allowedto randomly select the resource units, an unused value that is not usedas an AID is set in the corresponding AID field. Meanwhile, when theresource units to be used by the terminals are designated, AIDs assignedto the terminals are set in the corresponding AID fields. When unusedvalues that are not used as an AID are set in all of the n AID fields, nvalues set in these fields may and may not be a common value. Theterminal determines whether or not the value of the AID field is an“unused value that is not used as an AID.” When the “unused value thatis not used as an AID” (in the above-described example, a case of thebits whose zeroth to thirteenth bits indicate 0 or a value equal to orlarger than 2008 and whose fourteenth and fifteenth bits indicate “11”),then the terminal determines that the resource unit is available. Whenit is a value that can be used as the AID (in the above-describedexample, a case of bits whose zeroth to thirteenth bits indicate a valuefrom 1 to 2007 and whose fourteenth and fifteenth bits indicate “11”),the resource unit determines whether or not this AID is an AID of theterminal itself. When it is the AID of the terminal itself, then it isdetermined that use of this resource unit is designated for the terminalitself by the base station. When it is not the AID of the terminalitself, it is determined that this resource unit cannot be used by theterminal itself. The terminal, when there is any resource unitdesignated for the terminal itself, selects this resource unit. When thenumber of the resource units required for transmission is a pluralnumber (H units) and the number of the designated resource units is lessthan the value H, then resource unit or units in the number equal to thedifference should be randomly selected from among available resourceunits.

In accordance with the above-described second example, it is madepossible to restrict the UL-OFDMA candidate terminals to a particulargroup or groups and designate the resource units used by the terminalson a per-terminal basis. By virtue of this, for example, when theterminal uses a plurality of resource units, it is made possible todesignate some of the resource units by the base station while leavingthe remaining resource units randomly selected. With regard to theresource units designated by the base station, these resource units arenever used by other terminals, so that no interference occur between theterminals by that resource unit in the base station, and more reliablecommunications can be expected.

Third Example

In the second example, unused values that are not used as an AID, orAIDs assigned to the terminals are set in the AID fields. In thisexample, a value that is not assigned as an AID, or AIDs assigned to theterminals are set. The difference from the second example is explained.The values that are not assigned as an AID includes unused values thatis not used as an AID and further includes values which fall within therange that can be assigned by the base station as AIDs but are yet to beassigned as the AIDs. When the base station notifies a list of theterminals and the AIDs to each terminal, in this method as well, thesame or similar operation as that of the second example can beeffectuated. Specifically, the base station, when it makes the terminalsrandomly select the resource units, sets the values that are notassigned as an AID in the corresponding AID fields. Meanwhile, when thebase station designates the resource units to be used by the terminals,the AIDs assigned to the terminals are set in the corresponding AIDfields. The terminal determines whether or not a value of an AID fieldis “a value that is not assigned as an AID” using the above list. Whenit is “a value that is not assigned as an AID,” then the terminaldetermines that the corresponding resource unit is available. When it isa value that has already been assigned as an AID, the terminaldetermines whether or not this value is the AID of the terminal itself.When it is the AID of the terminal itself, then it is determined thatthe use of this resource unit is designated for the terminal itself bythe base station. When it is not the AID of the terminal itself, it isdetermined that this resource unit cannot be used by the terminalitself. The terminal, when there is any resource unit designated for theterminal itself, selects this resource unit. When the number of theresource units required for transmission is a plural number (H units)and the number of the designated resource units is less than the valueH, then resource unit or units in the number equal to the differenceshould be randomly selected from among available resource units.

In accordance with the above-described third example, the same orsimilar effect as that in the second example can be obtained.

Fourth Example

In the fourth example, the base station sets in the AID-fields the AIDsof the terminals for which use of the corresponding resource blocks areprohibited among the terminals that belong to the group of the group ID,or sets in the AID fields unused values that are not used as an AID. Thedifference from the first to third examples is explained. When use by aparticular terminal or terminals should be prohibited but use by any oneof the remaining terminals should be allowed, the AIDs of the terminalsthat should be prohibited from the use is set in the AID fields. Whenuse by any one of the terminals that belong to the group of the group IDshould be allowed, then the unused values that are not used as an AIDare set. In place of the unused values that are not used as an AID, inthe same manner as in the third example, values that are not assigned asan AID may be used. The terminal determines that the resource unit withthe AID of the terminal itself set in the AID field cannot be used bythe terminal itself. The terminal determines that the resource unit forwhich the unused value that is not used as an AID (or a value that isnot assigned as an AID) is set is available. The terminal randomlyselects the resource unit to be used by the terminal itself from amongthe available resource units.

In accordance with the above-described fourth example, it is madepossible to prohibit use of a certain resource unit or units by aparticular terminal or terminals and allow other terminals to randomlyselect the resource units.

Fifth Example

The fifth example differs from the first to fourth example in its modeof notification of the fact that the group ID is set in the Address 1field of the trigger frame.

It is considered here that the reason why it is necessary to notify thefact of the group ID being set in the Address 1 field is as follows: Innormal cases a unicast address, a broadcast address, or a multicastaddress is set in the Address 1 field and setting of a group ID is notexpected. Accordingly, it is necessary to make it possible todiscriminate the fact that a group ID is set in the Address 1 field fromthe fact that a broadcast or multicast address or the like is set.

In the first to fourth examples, in order to notify the fact that agroup ID is set, the Individual/Group bit of Address 2 field isconverted into 1. In this example, the Individual/Group bit remains tobe 0. Specifically, the MAC address (BSSID) of the base station is setin the Address 2 field as in the normal cases. Instead, the fact that agroup ID is set is notified to the terminal using another field. Forexample, presence or absence of the group ID is set using the reservedarea of the frame control field. Alternatively, the QoS fieldillustrated in FIG. 5 is retained in the trigger frame, and the presenceor absence of the group ID is set in the reserved area of the QoS field.Alternatively, a new field, for example, the HE (High Efficiency)control field illustrated in FIG. 11 is provided in the MAC header, andthe presence or absence of the group ID is set in the HE control field.This example is the same as or similar to the first to fourth exampleapart from the notification of the presence or absence of the group ID.

Sixth Example

In the sixth example, the method of notifying the fact that a group IDis set in the Address 1 field of the trigger frame is different fromthose in the first to fifth examples. This example is explained belowwith the focus given to the difference in relation to the fifth example.In the fifth example, in order to notify the fact that a group ID isset, the new field is provided or the reserved area of the existingfield is used. In contrast, in the sixth example, the AID field of theRU/AID field is used. In the AID field, the above-described “unusedvalue that is not used as an AID” is set in the AID field. The unusedvalues may be entered in all the AID fields or may be entered only inparticular one or a plurality of AID fields, for example, in the firstAID field. In the sixth example, the fact that the “unused value that isnot used as an AID” s set in the AID field indicates the fact that agroup ID is set in the Address 1 field. A “value that is not assigned asan AID” may be used in place of the “unused value that is not used as anAID.”

When the terminal receives the trigger frame (when it recognizes thatthe received frame is a trigger frame by the Type and the Subtype of theframe control field), the terminal checks either one of the AID fieldsor the value or values of the particular one or a plurality of AIDfields in the RU/AID field. When the value is an “unused value that isnot used as an AID” (or “a value that is not assigned as an AID”), thenthe terminal recognizes the fact that a group ID is set in the Address 1field. Alternatively, when the values of all the AID fields in theRU/AID field are checked and all of them are the “unused values that arenot used as an AID” (or “values that are not assigned as AIDs”), thenthe terminal may recognize the fact that a group ID is set in theAddress 1 field. When the terminal has recognized the fact that a groupID is set in the Address 1 field, the terminal reads the value set inthe Address 1 field and determines whether or not the terminal itselfbelongs to the group of the group ID indicated by the value. When theterminal itself belongs to the group, then the terminal identifies theresource unit indicated by the value set in each RU field of the RU/AIDfield as the resource unit that can be used by the terminal itself. Theterminal randomly selects the resource unit to be used by the terminalitself from among the identified resource units as has been previouslydescribed. The subsequent operations are the same as or similar to thefirst example.

Seventh Example

The seventh example uses the format of the trigger frame illustrated inFIG. 12 . The difference from the exemplary format illustrated in FIG. 9lies in the fact that the RU/AID field is substituted by an AIDNotification Field. The AID Notification field includes n AID fields(AID_1, AID_2 . . . AID_n). Each AID field is associated withcorresponding one of predetermined resource units. For example, theAID_1 is associated with the resource unit 1, the AID_2 is associatedwith the resource unit 2 and so forth. Correspondence of specific one ofthe AID fields to specific one of the resource units may be notified inadvance from the base station to each terminal, or may be defined inadvance by the system or the specification. The method of setting eachAID field and other fields are the same or similar to those that havebeen described in the foregoing. Also, the operation of the terminalwhen it has received the trigger frame is also the same as or similar tothat of the foregoing examples apart from the fact that the operation tocheck the RU field does not need to be done.

Eighth Example

The eighth example uses the format of the trigger frame illustrated inFIG. 13 . Difference from the exemplary format illustrated in FIG. 9lies in the fact that the RU/AID field is substituted by an RUNotification Field. The RU Notification Field includes n RU fields. Asin the same or similar manner as in the first to the sixth examples,identifiers of the resource units that can be used in UL-OFDMA are setin each of the RU fields. The method of setting other fields are thesame as or similar to those of the first example or fifth example.

For example, when the settings are made basically in accordance with thefirst example, a group ID is set in the Address 1 field and the MACaddress of the base station with the Individual/Group bit of 0substituted by 1 is set in the Address 2 field. Also, the Type of theframe control field is set as “Control” or “Management,” and a valueused for the Subtype is newly defined for the trigger frame.Alternatively, the Type may be set as “Data.” In this case, it may beconsidered that a field notifying whether or not it is a trigger frameis separately provided in the MAC header in place of defining a newvalue for the Subtype, and the bit is set in this field, and therebynotification of the fact that it is the trigger frame is performed.

Also, when the settings are done basically in accordance with the fifthexample, the group ID is set in the Address 1 field, and the MAC address(BSSID) of the base station is set in the Address 2. Also, presence orabsence of the group ID is set in the reserved area of the frame controlfield or the reserved area in the QoS field (see FIG. 5 ).Alternatively, an HE (High Efficiency) control field, for example,illustrated in FIG. 11 , is provided in the MAC header, and the presenceor absence of the group ID is set in the HE control field. Setting ofthe frame control field is the same as or similar to those of the abovefirst example, etc.

When the terminal receives the trigger frame (for example, recognizesthat the received frame is a trigger frame by the Type and the Subtypeof the frame control field), the terminal recognizes the availableresource unit or units from each RU field in the RU Notification Field,and randomly selects the resource unit or units from among therecognized resource units. The subsequent operations is the same orsimilar to those of the first example, etc.

Ninth Example

In the ninth example, in the same or similar manner as in the first tosixth examples, the format of the trigger frame illustrated in FIG. 9 isused, but the ninth example differs from the first to sixth examples inits usage of the Address 1 field and the AID field. In this example, abroadcast address or a multicast address is set in the Address 1 field.The frame in which the broadcast address is set is a frame that any oneof the terminals 1 to 8 receives as the frame addressed to the terminalitself. In the case of the multicast address set, it is assumed herethat the terminals 1 to 8 are the target terminals of the multicastaddress and receive the frame as it is addressed them. However, it isalso possible to use a multicast address of a group to which some of theterminals 1 to 8 do not belong. A group ID is set in each AID field inthe RU/AID field. The MAC address of the base station whoseIndividual/Group bit 0 is substituted by 1 is set in the Address 2 fieldin order to notify the fact that a group ID is set in each AID field. Inthe above-described other example, in order to notify the fact that agroup ID is set in the Address 1 field, the Individual/Group bit set to0 is converted into 1. In this example, however, in order to notify thefact that a group ID is set in the AID field, the Individual/Group bitis converted into 1. The group ID of the UL-OFDMA-eligible group is setin each AID field as the common value. FIG. 14 illustrates a state wherethe group ID is set in each AID field. The length of the group ID isdefined as two octets in the example of FIG. 14 in view of the originalpurpose of the AID field in which the AID is set, but the AID fieldlength may be modified if one octet is sufficient for representation ofthe group ID (for example, a case where the group ID consists of sixbits) such as configuring it as one-octet field. In this case,information that distinguishes the format from the format of FIG. 10 maybe set in the beginning of the RU/AID field, in the reserved area of anexisting field as described above, or in a newly added field or thelike.

When the terminal receives the trigger frame, the terminal determinesthat the frame is the one that should be received by the terminal itselfby the address of the Address 1 field of the received frame, andrecognizes that the received frame is a trigger frame by the Type andthe Subtype of the frame control field. Since the Individual/Group bitof the Address 2 field is 1, the fact that a group ID is set in the AIDfield is recognized. The terminal read the group ID from at least oneAID field and determines whether or not the group ID indicates the groupof the terminal itself. If it does not indicate the group of theterminal itself, the terminal determines that the terminal itself is notUL-OFDMA-eligible at this time and discards this frame. Meanwhile, ifthe above group ID indicates the group ID of the terminal itself, thenthe terminal reads the identifier of the resource unit from each RUfield and recognizes the available resource unit. And the terminalrandomly selects the resource set from among the recognized availableresource units.

The subsequent operations are the same as or similar to those of thefirst example, etc.

Tenth Example

The difference from the ninth example is explained below. In theabove-described ninth example, a common group ID is set in each of theAID fields, but in the tenth example, it is allowed to set differentgroup IDs for each of the AID fields. The base station decides on theavailable groups for each resource unit, and sets the group ID of therelevant Group in the AID field corresponding to the RU field.

When the terminal has received the trigger frame, the terminal detectsthe group ID set in each AID field and determines whether or not theterminal itself belongs to this group ID. The terminal recognizes onlythe resource units designated by the RU field corresponding to the AIDfield in which the group ID to which the terminal itself belongs is set,as the resource unit or units that can be used by the terminal itself.And the terminal randomly selects the resource unit from among therecognized available resource units. The subsequent operations are thesame as or similar to those of the first example, etc.

Eleventh Example

In the above-described ninth and tenth examples, the MAC address of thebase station whose Individual/Group bit 0 is substituted by 1 is set inthe Address 2 field in order to notify the fact that a group ID is setin each AID field. In contrast, in the eleventh example, the fact that agroup ID is set in each AID field is notified by a different method.

In the eleventh example, information notifying the fact that a group IDis set in each AID field (group ON information) is set in reserved areaof an existing field such as the reserved area of the frame controlfield, a newly defined field such as the HE control field illustrated inFIG. 11 , or the like. Alternatively, if an unused area (reserved area)exists in the RU field (for example, the area of the last two bits whenall the resource units can be discriminated by the higher six bits), thegroup ON information may be set in this area. When the group ONinformation is not set, the base station sets the AID in each AID field(in this case, as described above, UL-OFDMA is carried out with theterminals designated on a per-resource-unit basis). In this case, thebase station sets information (group OFF information) notifying the factthat the AID is set in the above area or in the new field or the like inplace of the group ON information. The MAC address (BSSID) of the basestation is set in the Address 2 field as in the normal cases. Abroadcast address or a multicast address is set in the Address 1 fieldin the same or similar manner as in the ninth example and the tenthexample.

The terminal that has received the trigger frame determines whether ornot the group ON information is set in the above-described existingreserve field or a newly defined field. When the group ON information isset, then the terminal recognizes the fact that a group ID (not an AID)is set in the AID field. The subsequent operations are the same orsimilar to those of the ninth or tenth example.

Twelfth Example

The twelfth example uses yet another method different from those of theninth to the eleventh examples to notify the fact that a group ID is setin each AID field. It is considered here that in the twelfth example, abroadcast address or a multicast address is set in the Address 1 fieldin the same or similar manner as in the ninth example and the tenthexample, and the MAC address (BSSID) of the base station is set in theAddress 2 field as in the normal cases.

In the twelfth example, the setting of the predetermined area in eachAID field is modified based on whether the group ID is set or the AID isset. For example, the when base station can describe the AID usingfourteen bits of the two octets (16 bits), then the fourteen bits of thezeroth to thirteenth bits are used to set the value of the AID or thegroup ID (which is assumed to have a shorter bit length than that of theAID), and the two bits of the fourteenth and fifteenth bits are used toidentify whether the group ID is set or the AID is set. For example whenthe AID is to be set, these two bits are set to “11” (group OFFinformation). When the group ID is to be set, these two bits are set to“00.” The bit setting described herein is an example and other bitsettings may also be considered.

When the terminal has received the trigger frame, the terminal checksthe predetermined area in each AID field (the fourteenth and fifteenthbit in this example). When the group ON information (for example, “00”)is set, the terminal recognizes the fact that a group ID is set in theAID field. When the group OFF information (for example, “11”) is set,the terminal recognizes the fact that the AID is set in the AID field.The operation after recognizing the fact that a group ID is set is thesame as or similar to those of the ninth example or the tenth example.

Thirteenth Example

In the first to twelfth examples, two modes of usage exist, i.e., a casewhere the group ID is set and another case where it is not set. Inaddition, when the group ID is set, Individual/Group bit of the Address2 field is set to 1, the information indicating the fact that a group IDis set (group ON information) is set in the reserved area of an existingfield, the newly defined field, or a predetermined area of the AIDfield. In contrast, in the thirteenth example, a Group ID field isdefined by default in the frame format. FIG. 15 illustrates the frameexemplary format of this case. The Group ID field is added between theSequence Control field and the RU/AID field. The length of the Group IDfield is given as one octet but not limited to this. The RU/AID fieldthat, for example, has the same configuration as that illustrated inFIG. 10 may be used. A predetermined value may be set in the AID fieldin the same or similar manner as in the first example (in a case wherethe terminal does not need to read the AID field).

Alternatively, when a particular resource unit is to be designated for aparticular terminal among the terminals that belongs to the groupdesignated by the Group ID field, the AID of the particular terminal maybe set in the AID field that corresponds to the RU field designating theparticular resource unit. In addition, an unused value that is not usedas an AID, or a value that is not assigned as an AID may be set in anAID field that corresponds to the RU field designating a resource unitwhich any terminal is allowed to use as long as it belongs to the group.

The AID set in each AID field may be a partial AID (which also appliesto the above-described other examples). The partial AID is part of theAID and it is assumed that overlapping of the partial AIDs does notoccur at least among the terminals belonging to the same group. Thepartial AID may be the one that is defined in the IEEE 802.11 standard.By using the partial AID in place of the AID, it is made possible toreduce the length of the AID field. For example, the length of the AIDfield can be modified from two octets to one octet. In this case, thesize of the RU/AID field can also be modified from 3×n to 2×n.

It is considered here that a broadcast or multicast address should beset in the Address 1 field and the MAC address (BSSID) of the basestation should be set in the Address 2 field as in the normal cases.Also, the setting of the frame control field should be made in the sameor similar manner as in the first to twelfth examples.

When the terminal has received the trigger frame, the terminaldetermines whether or not the terminal itself belongs to the groupdesignated in the Group ID field. When it belongs to the group, theterminal recognizes the available resource units from the value set ineach RU field set in the RU/AID field.

In addition, the terminal randomly selects the resource unit from amongthe recognized resource units based on the aforementioned behavior. Thesubsequent operations are the same as or similar to those of the otherexemplary operations. It is considered here that when the terminaldetermines that the terminal itself does not belong to the groupdesignated in the Group ID field, the terminal may make transition to asleep mode (power saving mode) for a predetermined period of time, suchas the period designated by the Duration/ID field. The operation to maketransition to the sleep mode is also applicable to the first tothirteenth examples.

Alternatively, when the terminal itself belongs to the group designatedby the Group ID field, the terminal examines the AID (or partial AID)set in the AID field and determines whether or not the terminal itselfis designated. When the terminal itself is designated, the terminaldetermines that the terminal itself uses the resource unit set in thecorresponding RU field. It is considered here that the number ofresource units designated for the terminal itself is less than H (aninteger equal to or larger than 1), the number of resource unitsrequired for transmission, the terminal identifies the RU field thatcorresponds to the AID field in which the unused value that is not usedas an AID or the value that is not assigned as an AID, and recognizesthat the resource unit designated by the RU field as an availableresource unit. In addition, resource units in the number correspondingto the value H subtracted by the actual number of the resource units maybe randomly additionally selected from among the recognized availableresource units.

Fourteenth Example

The fourteenth example uses the format of the trigger frame illustratedin FIG. 16 . It differs from that of FIG. 15 in that the RU/AID field issubstituted by an RU Notification Field. The configuration of the RUNotification Field is the same as or similar to that of FIG. 13 , andhas a form in which the AID field is omitted from the RU/AID field. Byusing this format, the same or similar operation as that of thethirteenth example where the AID field is ignored can be achieved withshorter trigger frame length.

Fifteenth Example

The fifteenth example uses the format of the trigger frame illustratedin FIG. 17 . It differs from that of FIG. 16 in that the RU NotificationField does not exist in it. It is assumed here that, when this format isused, the resource units that can be used in UL-OFDMA are defined inadvance and they are notified in advance from the base station to theterminal, or they are defined in advance by the system or thespecification. By virtue of this, the scheme for making each terminalrandomly designate the resource unit to perform UL-OFDMA can be achievedwith trigger frames with shorter frame lengths.

Sixteenth Example

In the foregoing explanations, terminals that have already beenconnected to the base station and have their AIDs assigned are treatedas being UL-OFDMA-eligible. However, it is also possible to designateany terminal that is not connected to the base station and has not anAID assigned as being UL-OFDMA-eligible. In this case, a certain groupID is defined for the terminal for which the AID is not designated.Accordingly, a terminal that has already been connected to the basestation does not belong to this group ID. The base station generates andtransmits a trigger frame in which this group ID is set on the basis ofany one of the above-described first to fifteenth examples. A terminalthat received the trigger frame and does not have an AID assignedthereto (terminal that is yet to be connected to the base station)determines that the terminal itself belongs to this group ID. Theterminal may be notified in advance about the notification of this groupID from the base station by a beacon frame or the like, or this group IDmay be defined by the system or the specification. The relevant terminalrandomly selects the resource unit as has been previously described. Thesizes of the resource units that can be used at this point may bedefined to be equal to each other. The terminal can carry out uplinktransmission of the association request frame by the selected resourceunit (in this case, the base station receives association request framessimultaneously from a plurality of terminals). The association requestframe is an example and other frames may be used such as a reassociationrequest frame, a probe request frame, and the like.

Also, in order to achieve the same or similar operation, instead ofusing a group ID for the terminal for which the AID is not designated,an unused value that is not used as an AID may be set in the AID fieldin any one of the above-described formats. In this case, the unusedvalue that is not used as an AID means, in contrast to theabove-described first to fifteenth examples, that a terminal for whichthe AID is not designated (terminal that has not yet been connected tothe base station) is designated. The terminal for which the AID is notdesignated recognizes in advance the range of the AID (for example, 1 to2007) by the system or the specification, and determines that values outof this range are values that are not used as the AIDs. When havingreceived the trigger frame, the terminal to which an AID is not assigned(terminal that has not yet been connected to the base station)determines that the terminal itself is designated if an unused valuethat is not used as an AID is set in any one of the AID fields. And theterminal randomly selects the resource unit and is allowed to carry outuplink transmission of frames such as the association request frameusing the selected resource unit.

It is considered here that an UL-OFDMA can also be implemented thatinvolves both the terminal for which the AID is not designated and theterminal for which the AID is designated as described in the first tofifteenth examples. In this case, it can be readily implemented bycombining the sixteenth example with any one or a plurality of the firstto fifteenth examples.

Seventeenth Example

The group ID may be provided for terminals carrying out power saving andit may be designated by the trigger frame. For example, suppose herethat in some cases a terminal carrying out power saving periodicallysends a particular frame to the base station. For example, this mayimply that the terminal is requested to periodically send PS-Poll. Inview of this, in accordance with the timing, the base station may beadapted to transmit a trigger frame that designates the group ID ofterminals carrying out power saving and receive a particular frame froma plurality of terminals. The individual terminals does not need tocarry out processes such as acquisition of the access right by carriersense and back-off in contrast to a case of a conventional single usertransmission, which makes it possible to achieve further reduction inthe power consumption.

Eighteenth Example

The above-described frame formats illustrated in FIGS. 9 to 17 areexemplary formats and other fields may exist in the trigger frame. Forexample, there may be provided a field for setting informationdesignating the packet length (PPDU length) of the physical packettransmitted by UL-OFDMA. An MCS (modulation coding method) used inUL-OFDMA or information designating the data rate may be set as well.The packet length, the MCS, or both of them may be the same for all theterminals belonging to the group designated by the group ID or may beindividually designated for each of the terminals belonging to thisgroup. Alternatively, designation of the MCS may be performed on aper-resource-unit basis. The field in which the above-describedinformation is set may be located at any position within the triggerframe. For example, it may exist in the HE Control field as illustratedin FIG. 11 , in the frame body field, or in the RU/AID field. Theexamples described herein are examples and other fields for settingvarious pieces of information may be provided.

Combinations of First to Eighteenth Examples

The above-described first to eighteenth examples can be independentlyimplemented and two or more of these examples may be combined asappropriate as long as inconsistency does not occur in their operations.For example, by combining the thirteenth example and the fourth example,an AID of the terminal for which use of the resource block is prohibitedmay be set in the AID field in the thirteenth example. Combinationsother than this are also possible.

FIG. 18 illustrates a flowchart of one example of the operation of thebase station in accordance with the embodiment of the present invention.When the base station has decided to start UL-OFDMA at a predeterminedtiming, the base station determines, as the method of designating theUL-OFDMA-eligible terminals, whether it uses the individual designationmethod that individually designates the individual terminals or thegroup designation method that designates the group (S101). It isconsidered here that the determination of the method may be performedprior to start of UL-OFDMA or either one of them may be determined inadvance.

When the individual designation method has been decided (NO in the stepS102), the individual terminals for which UL-OFDMA is carried out thistime are selected from among the OFDMA-compliant terminals that arecurrently connected to the base station and the resource units assignedto each of the terminals are decided (S103). Any methods may be used asthe method of selecting the individual terminals. For example, presenceor absence of an UL-OFDMA request from each terminal may be collectedand the terminals may be selected from the terminals having therequests. Alternatively, on the basis of the data amount fortransmission by each terminal, terminals having the largest data amountmay be preferentially selected, or terminals having the same or similardata amounts may be selected. Also, the terminals may be selected fromamong the terminals belonging to the same group. At this point, as thecriteria for selecting the group, items may be taken into account suchas presence or absence of the UL-OFDMA transmission request from eachterminal belonging to each group and the transmission data amount.Alternatively, the terminals or groups may be selected by round-robin,or terminals or groups may be randomly selected. Alternatively, it isalso possible to select a terminal having a data whose subsequent datato be transmitted is estimated to have the same or similar size orselect terminals whose periods of generation of data are the same as orsimilar to each other (terminals whose data generation periods fallwithin a predetermined range of values, or a predetermined number ofterminals whose data generation periods are the closest to each other,etc.). Alternatively, the spatial channel characteristics with eachterminal may be recognized in advance, and on the basis of the spatialchannel characteristics, combination of terminals having a small spatialcorrelation (exhibiting less interference) may be selected. It isconsidered here that the number of terminals to be selected is up to themaximum number of available resource units. Meanwhile, when theabove-described OFDMA&MIMO scheme is used, it is possible to selectterminals in the number that is larger than the maximum resource unitnumber. When a lower limit is set for the number of terminals to beselected, terminals in the number equal to or larger than the lowerlimit may be selected. The examples of the section of the terminals aremerely examples and methods other than those described herein may beused to select the terminals.

Also, the method of assigning the resource units may be performed asappropriate. For example, when the resource units are all on the samebandwidth and one resource unit is assigned to each terminal, any one ofthe resource units may be assigned to each terminal. Also, when thereexist resource units of different bandwidths, a resource unit of largerbandwidth may be assigned to a terminal of larger data amount. Also,when more than one resource unit is assigned to one terminal, resourceunits consecutively arranged on the frequency domain may be selected,and it is also possible to select non-continuously arranged resourceunits.

It is considered here that the band used in UL-OFDMA uplink transmissionmay be defined in advance by the system or the specification, or may bedetermined by the base station when performing UL-OFDMA. Alternatively,it may be determined by any methods other than those mentioned herein.

The base station sets, in the predetermined fields of the trigger frame,the identifier of the selected terminal (AID, etc.) and the identifierof the resource unit assigned to this terminal (S104). The predeterminedfields depend on the formats in use. In the format of FIG. 10 , thepredetermined fields are the RU field and the AID field in the RU/AIDfield. A broadcast address or a multicast address is set in the Address1 field as the RA. Also, the MAC address (BSSID) of the station itselfis set in the Address 2 field. Also, values for the trigger frame may beset in the Type field and the Subtype field of the frame control field.It is considered here that the identifier of the resource unit may beunique values for bands such as 20 MHz, 40 MHz, 80 MHz, etc. or it maybe allowed to use an identifier having the same value for differentbands. When it is allowed to use the identifier having the same valuefor different bands, information discriminating a used band or bandsfrom the other bands should be notified in the trigger frame (forexample, HE Control field of FIG. 11 , etc.) in addition to theidentifier of the resource unit or the band to be used may be notifiedin advance to the terminal.

The base station, when having generated the trigger frame, acquires theaccess right to access the wireless medium in accordance with CSMA/CA,and transmits the trigger frame (more specifically, a physical packetincluding the trigger frame) on the basis of the acquired access right(S105). The trigger frame is, for example, transmitted by the channel ofthe basic channel width (for example, 20 MHz) with which a legacyterminal can also perform transmission and reception.

Here, the band used in the UL-OFDMA uplink transmission is a band onwhich the trigger frame was transmitted. If the band for the uplinktransmission is 20 MHz, this is the same band as that on which thetrigger frame was transmitted. When the band of the uplink transmissionis 40 MHz, the transmission of the trigger frame may be respectivelydone on two channels each having a 20 MHz width within the 40 MHz width.Also, when the band of the uplink transmission is 80 MHz, thetransmission of the trigger frame may be respectively done on fourchannels each having a 20 MHz width within the 80 MHz width. These modesare illustrated in FIG. 19 . The contents of the trigger frames can bethe same. After the step S105, the process may go back to the step S101or S102.

Meanwhile, the base station, when having decided on the groupdesignation method, selects the group that is allowed for the UL-OFDMAof this time from among one or more groups generated by sorting thecurrently connected OFDMA-compliant terminals (S106). Any methods may beused as the method of selecting the group. For example, presence orabsence of an UL-OFDMA request from each terminal may be collected andthe group may be selected that includes the terminals having therequests. Alternatively, on the basis of the data amount fortransmission by each terminal, a group including terminals having thelargest data amount may be selected, or the group that includes thelargest number of terminals having the same or similar data amounts maybe selected. Alternatively, the group may be selected by round-robin, orthe group may be randomly selected. Alternatively, it is also possibleto select the group that includes the largest number of the terminalhaving a data whose subsequent data to be transmitted is estimated tohave the same or similar size or select terminals whose periods ofgeneration of data are the same as or similar to each other (terminalswhose data generation periods fall within a predetermined range ofvalues, or a predetermined number of terminals whose data generationperiods are the closest to each other, etc.). It is considered here thatone single group is selected, but as described above, it is alsopossible to select a plurality of groups. The examples of the selectionof the group described herein are merely examples and methods other thanthose described herein may be used to select the group.

It is considered here that the band used in UL-OFDMA uplink transmissionmay be defined in advance by the system or the specification, or may bedetermined by the base station when performing UL-OFDMA. Alternatively,it may be determined by any methods other than those mentioned herein.

The base station sets the group ID of the selected group in thepredetermined field of the trigger frame (S107). The predetermined fielddepends on the formats to be used and their mode of usage and, forexample, is the RA field (Address 1 field) in the case of the format ofFIG. 10 . Also, the MAC address (BSSID) of the station itself with theIndividual/Group bit inverted from 0 to 1 is set in the Address 2 field.Also, values for the trigger frame may be set in the Type field and theSubtype field of the frame control field. They may be set by methodsother than those described herein, and formats other than the format ofFIG. 10 may be used. Since the details have already been explained,further explanations are omitted. Also, the base station may setinformation discriminating a used band or bands in the trigger frame(for example, in the HE Control field of FIG. 11 , etc.) or notify it inadvance by another frame, or the band to be used may be defined inadvance by the system or the specification. Alternatively, notificationof the band or bands to be used may be implicitly notified in accordancewith the channels (bands) on which the trigger frames are received. Forexample, when the channel of the basic channel width of 20 MHz is usedin the uplink transmission, as illustrated in FIG. 19 mentioned above,the trigger frame is transmitted on this channel. When the channel of 40MHz width is used, the transmission of the trigger frame may berespectively done on two channels each having a 20 MHz width included inthe 40 MHz width. Also, when the channel of 80 MHz width is used, thetransmission of the trigger frame is respectively done on four channelseach having a 20 MHz width within the 80 MHz width. The terminal on thereception side determines that the uplink transmission is possible onthe channel (band) on which the trigger frame was received. It isconsidered here that when reception of the trigger frame was successfulin some of the channels on the side of the terminals but failed in otherchannels, the resource units to be selected may be restricted such thatonly the resource units included in the reception-successful channels(bands) are selected.

When the base station has generated the trigger frame, the base stationacquires the access right to the wireless medium in accordance withCSMA/CA and transmits a trigger frame (more specifically, a physicalpacket including the trigger frame) on the basis of the acquired accessright (S105). The details of the step S105 are as described above. Afterthe step S105, the process may go back to the step S101 or S102.

In the explanation of the group designation method of FIG. 18 ,selection of the terminal and assignment of the resource unit may beperformed in addition to the selection of the group. In this case, thegroup ID is set in the trigger frame, and the pair of the identifier(AID, etc.) of the selected terminal and the identifier of the resourceunit is set in the trigger frame, by virtue of which the resource unitmay be designated for the selected terminal. It is considered here thatthe terminal to be selected may be a terminal that belongs to theselected group, or may be selected from another group other than theselected group. Also, it may be considered that the terminal for whichimplementation of UL-OFDMA is prohibited is selected within the groupand the identifier of the selected terminal is set in the trigger frameso as to ensure that the selected terminal cannot perform the selectionof the resource unit and the uplink transmission. The operationsdescribed herein are only examples and various modified operations arepossible to realize the above-described first to seventeenth examplesand the combinations thereof.

FIG. 20 illustrates a flowchart of an example of the operation of theterminal in accordance with the embodiment of the present invention.When the terminal has received the trigger frame transmitted from thebase station (S201), the terminal determines, on the basis of theinformation set in the trigger frame, whether the individual designationmethod individually designating individual terminals is designated orthe group designation method designating a group is specified (S202).The method of determination varies depending on the formats of thetrigger frame and their mode of usage. For example, when theIndividual/Group bit in the Address 2 field is set to 1, it isdetermined that the designation method is the group designation method,and if it is set to 0, then it is determined that the designation methodis the individual designation method. Alternatively, the determinationis made on the basis of the predetermined field in which the informationis set for identifying either the group designation method or theindividual designation method. Another configuration is also possiblefor the determination to be made in accordance with methods other thanthose described herein. The details are as described in the foregoing.

When the individual designation method is designated (NO in the stepS202), it is determined whether or not the terminal itself is designatedas the UL-OFDMA-eligible terminal (S203). For example, when the AID ofthe terminal itself is set in the AID field, it is determined that theterminal itself is designated. When the terminal itself is designated,the resource unit assigned to the terminal itself is identified (S204).For example, the resource unit designated in the RU field correspondingto the AID field in which the AID of the terminal itself is set isidentified as the resource unit assigned to the terminal itself. Theterminal generates frames such as data frame for uplink transmission andthe like and performs the transmission with the identified resource unitafter the elapse of a predetermined time period after the completion ofthe reception of the trigger frame (S205). When conditions such as thetransmission packet length (PPDU length), MCS, etc. are designated inthe trigger frame, generation and transmission of the frames areperformed such that these conditions are satisfied.

Meanwhile, when the group designation method is designated (YES in thestep S202), the group ID is read from the predetermined field of thetrigger frame and it is determined whether or not the terminal itselfbelongs to the group indicated by the group ID (S206). The predeterminedfield in which the group ID is set varies depending on the formats ofthe trigger frame and their mode of usage. For example, the group ID isset in the RA field (Address 1 field). Alternatively, a configuration inwhich the group ID is set in the AID field and another configuration inwhich the group ID is set in the HE Control field of FIG. 11 are alsopossible. Details are as described in the foregoing. When the terminalitself belongs to the above group, the terminal randomly selects theresource unit from among a plurality of resource units that becomes thecandidates (S207). Between the steps S206 and S207, a step may be addedfor determining whether the terminal has a right to select the resourceunit. For example, a value of the backoff counter which was randomlyselected in advance is subtracted by the number of the resource unitsthat becomes the candidates, and when the resultant value is zero orless, the terminal acquires the right to select the resource unit andthe processing proceeds to the step S207. When the resultant value ismore than zero, the terminal cannot acquire the right to select theresource unit and the processing ends or returns to the step S201. Theresource units that become the candidates are designated by the RU fieldor the like of the trigger frame. Also, when a plurality of group IDsare set in the trigger frame and different resource units that becomethe candidates are designated for each of the group ID, then theterminal identifies the resource unit that becomes the candidateassociated with the group ID to which the terminal itself belongs.Alternatively, the resource units that become the candidates may bedefined in advance by the system or the specification or the like.Alternatively, when identification information identifying a set of theresource units that become the candidates is set in the trigger frame,then the resource units that become the candidate may be identified fromthe identification information that is set and the correspondenceinformation associating the identification information with the resourceunits (a table, etc.). The correspondence information may be notified inadvance by the base station. The number of resource units to be randomlyselected may be defined in advance, or information designating thenumber of the units to be selected may be set in the trigger frame. Theterminal generates a frame such as a data frame for uplink transmissionand transmits it in the randomly selected resource unit after the elapseof a predetermined time period after the completion of the reception ofthe trigger frame (S205). When conditions such as the transmissionpacket length (PPDU length), MCS, etc. are designated in the triggerframe, generation and transmission of the frames are performed such thatthese conditions are satisfied.

It is considered here that, when it has been determined that the groupID is designated in the step S202, a configuration is also possibleaccording to which whether or not individual designation of the resourceunit is made for the terminal itself is checked in addition to thedetermination regarding whether or not the terminal itself belongs tothe above group. In this case, the terminal uses the designated resourceunit even when it belongs to the above group. In other words, the otherterminals, when there is any resource unit that is designated for theterminal, randomly select from among the resource units that becomecandidates other than the resource unit. Also, when the terminal itselfwhich belongs to the group is designated as the UL-OFDMA-prohibitedterminal, the terminal itself is adapted to not perform the selection ofthe resource unit and the uplink transmission. When the prohibitedterminals are designated for each resource unit, random selection is tobe made from among the resource units other than the designated resourceunit in the random selection of the resource unit. Details thereof areas described in the foregoing. The operations described herein aremerely examples and various modified operations are possible to realizethe above-described first to seventeenth examples and the combinationsthereof.

According to this embodiment, efficient communications are carried outby designating resource units for each terminal for example in a casewhere presence or absence of the uplink requests can be accuratelygrasped, and otherwise the terminals are designated by the group ID soas to suppress the number of terminals that become the transmissioncandidates appropriately, and to reduce the likelihood of a plurality ofterminals simultaneously using the same resource unit. By virtue ofthis, it is made possible to suppress deterioration in efficiency ofutilizing the resource. Also, when UL-OFDMA is carried out in a casewhere existence of terminals in power saving and presence of uplinktransmission requests are not sufficiently grasped, increase inefficiency of utilizing the resource can be expected by designation ofthe group ID compared with the case of designation of individualterminals. In particular, this effect is expected to be large when thenumber of terminals belonging to the group is larger than the number ofterminals to be designated in the case of the individual designation.Meanwhile, when the number of the terminals is too large, probability ofcollision between terminals within the resource units will increase.Accordingly, the relationship between the number of terminals belongingto the group and the number of resource units may be adjusted such thatthe number of the resource units becomes sufficiently large relative tothe number of terminals belonging to the group. As one example, thenumber of resource units is adjusted such that the number of resourceunits becomes sufficiently large relative to the number of terminalsbelonging to the same group ID. The number of the resource units shouldbe at least larger than the number of terminals belonging to the groupID. For example, the number of resource units may be defined as2{circumflex over ( )}(the number of terminals belonging to the groupID)−1 or larger than that (for example, a case is considered where theterminal selects one resource unit). If the number of terminalsbelonging to the group ID is 4, then the number of resource units is setto be equal to or larger than 15 (=2{circumflex over ( )}4−1). As hasbeen previously described, other techniques such as to limit the numberof terminals belonging to the same group to access the resource unitsmay be used in combination. Also, in this embodiment, the same frameformat (FIG. 10 , etc.) can be diverted for the individual designationmethod and the group designation method.

It is considered here that this embodiment presents use of the triggerframe having the same format in different modes (for example, a modeaccording to which the resource units are individually designated foreach terminal and another mode according to which the group ID isdesignated and the resource units used by the terminals are randomlyselected on the side of the terminals), but there is no problem when theframe format of the trigger frame is adapted for either one of these twomodes.

The difference between the configuration where transmission is performedusing the resource units randomly selected by the terminals designatedby the group ID in this embodiment and the Restricted Access Window(RAW) operation defined in the IEEE 802.11ah standard is explained. Inthe RAW operation, when one time slot is defined as a resource unit, aterminal is designated and assigned to the time slot or a groupidentifier is assigned thereto. Each terminal attempts to make an accessfrom the time slot boundary (even when the terminal is designated) inaccordance with CSMA/CA-based EDCA (Enhanced Distributed ChannelAccess). Meanwhile, this embodiment provides a plurality of resourceunits on the frequency domain, and terminals are designated for each ofthem, or the group indicated by the group identifier (a plurality ofterminals) is collectively assigned to these resource units. And eachterminal randomly selects one resource unit from a plurality of resourceunits in the frequency domain and transmits the frames after the elapseof a predetermined time after the completion of the reception of thetrigger frame. Accordingly, in the RAW operation of the IEEE 802.11ahstandard, CSMA/CA-based EDCA is carried out and thereby collisionavoidance function works on each terminal. In contrast, in thisembodiment, this function does not work. Accordingly, in thisembodiment, in order to avoid occurrence of collision, it becomes moreimportant to adjust the number of resource units on the frequency domainrelative to the number of terminals expected to perform transmission asdescribed above.

The above-stated group ID is merely one example, and may be otherconfiguration. For example, the group ID may be a multicast address. Inthe above embodiment, the group identified by the group ID is a group ofterminals which have been associated with the base station. Also, theAID may be used as the group ID. In that case, a value used as the groupID may be an unused value not assigned to associated terminals as theAIDs (i.e., a value less than 1 or larger than 2007). For example, AID 0may identify terminals) which have not yet been associated with the basestation.

Second Embodiment

FIG. 21 is a functional block diagram of a base station (access point)400 according to a second embodiment. The access point includes acommunication processor 401, a transmitter 402, a receiver 403, antennas42A, 42B, 42C, and 42D, a network processor 404, a wired I/F 405, and amemory 406. The access point 400 is connected to a server 407 throughthe wired I/F 405. The communication processor 401 has functions similarto the MAC processor 10 and the MAC/PHY manager 60 described in thefirst embodiment. The transmitter 402 and the receiver 403 havefunctions similar to the PHY processor 50 and the analog processor 70described in the first embodiment. The network processor 404 hasfunctions similar to the higher processor 90 described in the firstembodiment. The communication processor 401 may internally possess abuffer for transferring data to and from the network processor 404. Thebuffer may be a volatile memory, such as an SRAM or a DRAM, or may be anon-volatile memory, such as a NAND or an MRAM.

The network processor 404 controls data exchange with the communicationprocessor 401, data writing and reading to and from the memory 406, andcommunication with the server 407 through the wired I/F 405. The networkprocessor 404 may execute a higher communication process of the MAClayer, such as TCP/IP or UDP/IP, or a process of the application layer.The operation of the network processor may be performed throughprocessing of software (program) by a processor, such as a CPU. Theoperation may be performed by hardware or may be performed by both ofthe software and the hardware.

For example, the communication processor 401 corresponds to a basebandintegrated circuit, and the transmitter 402 and the receiver 403correspond to an RF integrated circuit that transmits and receivesframes. The communication processor 401 and the network processor 404may be formed by one integrated circuit (one chip). Parts that executeprocessing of digital areas of the transmitter 402 and the receiver 403and parts that execute processing of analog areas may be formed bydifferent chips. The communication processor 401 may execute a highercommunication process of the MAC layer, such as TCP/IP or UDP/IP.Although the number of antennas is four here, it is only necessary thatat least one antenna is included.

The memory 406 saves data received from the server 407 and data receivedby the receiver 402. The memory 406 may be, for example, a volatilememory, such as a DRAM, or may be a non-volatile memory, such as a NANDor an MRAM. The memory 406 may be an SSD, an HDD, an SD card, an eMMC,or the like. The memory 406 may be provided outside of the base station400.

The wired I/F 405 transmits and receives data to and from the server407. Although the communication with the server 407 is performed througha wire in the present embodiment, the communication with the server 407may be performed wirelessly. In this case, a wireless I/F may beemployed instead of the wired I/F 405.

The server 407 is a communication apparatus that returns a responseincluding requested data in response to reception of a data forwardrequest for requesting transmission of the data. Examples of the server407 include an HTTP server (Web server) and an FTP server. However, theserver 407 is not limited to these as long as, the server 407 has afunction of returning the requested data. The server 407 may be acommunication apparatus operated by the user, such as a PC or asmartphone.

When the STA belonging to the BSS of the base station 400 issues aforward request of data for the server 407, a packet regarding the dataforward request is transmitted to the base station 400. The base station400 receives the packet through the antennas 42A to 42D. The basestation 400 causes the receiver 403 to execute the process of thephysical layer and the like and causes the communication processor 401to execute the process of the MAC layer and the like.

The network processor 404 analyzes the packet received from thecommunication processor 401. Specifically, the network processor 404checks the destination IP address, the destination port number, and thelike. When the data of the packet is a data forward request such as anHTTP GET request, the network processor 404 checks whether the datarequested by the data forward request (for example, data in the URLrequested by the HTTP GET request) is cached (stored) in the memory 406.A table associating the URL (or reduced expression of the URL, such as ahash value or an identifier substituting the URL) and the data is storedin the memory 406. The fact that the data is cached in the memory 406will be expressed that the cache data exists in the memory 406.

When the cache data does not exist in the memory 406, the networkprocessor 404 transmits the data forward request to the server 407through the wired I/F 405. In other words, the network processor 404substitutes the STA to transmit the data forward request to the server407. Specifically, the network processor 404 generates an HTTP requestand executes protocol processing, such as adding the TCP/IP header, totransfer the packet to the wired I/F 405. The wired I/F 405 transmitsthe received packet to the server 407.

The wired I/F 405 receives, from the server 407, a packet that is aresponse to the data forward request. From the IP header of the packetreceived through the wired I/F 405, the network processor 404 figuresout that the packet is addressed to the STA and transfers the packet tothe communication processor 401. The communication processor 401executes processing of the MAC layer and the like for the packet. Thetransmitter 402 executes processing of the physical layer and the likeand transmits the packet addressed to the STA from the antennas 42A to42D. The network processor 404 associates the data received from theserver 407 with the URL (or reduced expression of the URL) and saves thecache data in the memory 406.

When the cache data exists in the memory 406, the network processor 404reads the data requested by the data forward request from the memory 406and transmits the data to the communication processor 401. Specifically,the network processor 404 adds the HTTP header or the like to the dataread from the memory 406 and executes protocol processing, such asadding the TCP/IP header, to transmit the packet to the communicationprocessor 401. In this case, the transmitter IP address of the packet isset to the same IP address as the server, and the transmitter portnumber is also set to the same port number as the server (destinationport number of the packet transmitted by the communication terminal),for example. Therefore, it can be viewed from the STA as ifcommunication with the server 407 is established. The communicationprocessor 401 executes processing of the MAC layer and the like for thepacket. The transmitter 402 executes processing of the physical layerand the like and transmits the packet addressed to the STA from theantennas 42A to 42D.

According to the operation, frequently accessed data is responded basedon the cache data saved in the memory 406, and the traffic between theserver 407 and the base station 400 can be reduced. Note that theoperation of the network processor 404 is not limited to the operationof the present embodiment. There is no problem in performing otheroperation when a general caching proxy is used, in which data isacquired from the server 407 in place of the STA, the data is cached inthe memory 406, and a response is made from the cache data of the memory406 for a data forward request of the same data.

The base station (access point) of the present embodiment can be appliedas the base station of the first embodiment.

In the present embodiment, although the base station with the cachefunction is described, a terminal (STA) with the cache function can alsobe realized by the same block configuration as FIG. 21 . In this case,the wired I/F 405 may be omitted.

Third Embodiment

FIG. 22 shows an example of entire configuration of a terminal or a basestation. The example of configuration is just an example, and thepresent embodiment is not limited to this. The terminal or the basestation includes one or a plurality of antennas 1 to n (n is an integerequal to or greater than 1), a wireless LAN module 148, and a hostsystem 149. The wireless LAN module 148 corresponds to the wirelesscommunication apparatus according to the first embodiment. The wirelessLAN module 148 includes a host interface and is connected to the hostsystem 149 through the host interface. Other than the connection to thehost system 149 through the connection cable, the wireless LAN module148 may be directly connected to the host system 149. The wireless LANmodule 148 can be mounted on a substrate by soldering or the like andcan be connected to the host system 149 through wiring of the substrate.The host system 149 uses the wireless LAN module 148 and the antennas 1to n to communicate with external apparatuses according to an arbitrarycommunication protocol. The communication protocol may include theTCP/IP and a protocol of a layer higher than that. Alternatively, theTCP/IP may be mounted on the wireless LAN module 148, and the hostsystem 149 may execute only a protocol in a layer higher than that. Inthis case, the configuration of the host system 149 can be simplified.Examples of the present terminal include a mobile terminal, a TV, adigital camera, a wearable device, a tablet, a smartphone, a gamedevice, a network storage device, a monitor, a digital audio player, aWeb camera, a video camera, a projector, a navigation system, anexternal adaptor, an internal adaptor, a set top box, a gateway, aprinter server, a mobile access point, a router, an enterprise/serviceprovider access point, a portable device, and a hand-held device.

FIG. 23 shows an example of hardware configuration of a wireless LANmodule. The configuration can also be applied when the wirelesscommunication apparatus is mounted on either one of the terminal that isa non-base station and the base station. Therefore, the configurationcan be applied as an example of specific configuration of the wirelesscommunication apparatus shown in FIG. 1 . At least one antenna 247 isincluded in the example of configuration. When a plurality of antennasare included, a plurality of sets of a transmission system (216 and 222to 225), a reception system (232 to 235), a PLL 242, a crystaloscillator (reference signal source) 243, and a switch 245 may bearranged according to the antennas, and each set may be connected to acontrol circuit 212. One or both of the PLL 242 and the crystaloscillator 243 correspond to an oscillator according to the presentembodiment.

The wireless LAN module (wireless communication apparatus) includes abaseband IC (Integrated Circuit) 211, an RF (Radio Frequency) IC 221, abalun 225, the switch 245, and the antenna 247.

The baseband IC 211 includes the baseband circuit (control circuit) 212,a memory 213, a host interface 214, a CPU 215, a DAC (Digital to AnalogConverter) 216, and an ADC (Analog to Digital Converter) 217.

The baseband IC 211 and the RF IC 221 may be formed on the samesubstrate. The baseband IC 211 and the RF IC 221 may be formed by onechip. Both or one of the DAC 216 and the ADC 217 may be arranged on theRF IC 221 or may be arranged on another IC. Both or one of the memory213 and the CPU 215 may be arranged on an IC other than the baseband IC.

The memory 213 stores data to be transferred to and from the hostsystem. The memory 213 also stores one or both of information to betransmitted to the terminal or the base station and informationtransmitted from the terminal or the base station. The memory 213 mayalso store a program necessary for the execution of the CPU 215 and maybe used as a work area for the CPU 215 to execute the program. Thememory 213 may be a volatile memory, such as an SRAM or a DRAM, or maybe a non-volatile memory, such as a NAND or an MRAM.

The host interface 214 is an interface for connection to the hostsystem. The interface can be anything, such as UART, SPI, SDIO, USB, orPCI Express.

The CPU 215 is a processor that executes a program to control thebaseband circuit 212. The baseband circuit 212 mainly executes a processof the MAC layer and a process of the physical layer. One or both of thebaseband circuit 212 and the CPU 215 correspond to the communicationcontrol apparatus that controls communication or the controller thatcontrols communication.

At least one of the baseband circuit 212 and the CPU 215 may include aclock generator that generates a clock and may manage internal time bythe clock generated by the clock generator.

For the process of the physical layer, the baseband circuit 212 performsaddition of the physical header, coding, encryption, modulation process,and the like of the frame to be transmitted and generates, for example,two types of digital baseband signals (hereinafter, “digital I signal”and “digital Q signal”).

The DAC 216 performs DA conversion of signals input from the basebandcircuit 212. More specifically, the DAC 216 converts the digital Isignal to an analog I signal and converts the digital Q signal to ananalog Q signal. Note that a single system signal may be transmittedwithout performing quadrature modulation. When a plurality of antennasare included, and single system or multi-system transmission signalsequivalent to the number of antennas are to be distributed andtransmitted, the number of provided DACs and the like may correspond tothe number of antennas.

The RF IC 221 is, for example, one or both of an RF analog IC and a highfrequency IC. The RF IC 221 includes a filter 222, a mixer 223, apreamplifier (PA) 224, the PLL (Phase Locked Loop) 242, a low noiseamplifier (LNA) 234, a balun 235, a mixer 233, and a filter 232. Some ofthe elements may be arranged on the baseband IC 211 or another IC. Thefilters 222 and 232 may be bandpass filters or low pass filters. The RFIC 221 is connected to the antenna 247 through the switch 245.

The filter 222 extracts a signal of a desired band from each of theanalog I signal and the analog Q signal input from the DAC 216. The PLL242 uses an oscillation signal input from the crystal oscillator 243 andperforms one or both of division and multiplication of the oscillationsignal to thereby generate a signal at a certain frequency synchronizedwith the phase of the input signal. Note that the PLL 242 includes a VCO(Voltage Controlled Oscillator) and uses the VCO to perform feedbackcontrol based on the oscillation signal input from the crystaloscillator 243 to thereby obtain the signal at the certain frequency.The generated signal at the certain frequency is input to the mixer 223and the mixer 233. The PLL 242 is equivalent to an example of anoscillator that generates a signal at a certain frequency.

The mixer 223 uses the signal at the certain frequency supplied from thePLL 242 to up-convert the analog I signal and the analog Q signal passedthrough the filter 222 into a radio frequency. The preamplifier (PA)amplifies the analog I signal and the analog Q signal at the radiofrequency generated by the mixer 223, up to desired output power. Thebalun 225 is a converter for converting a balanced signal (differentialsignal) to an unbalanced signal (single-ended signal). Although thebalanced signal is handled by the RF IC 221, the unbalanced signal ishandled from the output of the RF IC 221 to the antenna 247. Therefore,the balun 225 performs the signal conversions.

The switch 245 is connected to the balun 225 on the transmission sideduring the transmission and is connected to the balun 234 or the RF IC221 on the reception side during the reception. The baseband IC 211 orthe RF IC 221 may control the switch 245. There may be another circuitthat controls the switch 245, and the circuit may control the switch245.

The analog I signal and the analog Q signal at the radio frequencyamplified by the preamplifier 224 are subjected to balanced-unbalancedconversion by the balun 225 and are then emitted as radio waves to thespace from the antenna 247.

The antenna 247 may be a chip antenna, may be an antenna formed bywiring on a printed circuit board, or may be an antenna formed by usinga linear conductive element.

The LNA 234 in the RF IC 221 amplifies a signal received from theantenna 247 through the switch 245 up to a level that allowsdemodulation, while maintaining the noise low. The balun 235 performsunbalanced-balanced conversion of the signal amplified by the low noiseamplifier (LNA) 234. The mixer 233 uses the signal at the certainfrequency input from the PLL 242 to down-convert, to a baseband, thereception signal converted to a balanced signal by the balun 235. Morespecifically, the mixer 233 includes a unit that generates carrier wavesshifted by a phase of 90 degrees based on the signal at the certainfrequency input from the PLL 242. The mixer 233 uses the carrier wavesshifted by a phase of 90 degrees to perform quadrature demodulation ofthe reception signal converted by the balun 235 and generates an I(In-phase) signal with the same phase as the reception signal and a Q(Quad-phase) signal with the phase delayed by 90 degrees. The filter 232extracts signals with desired frequency components from the I signal andthe Q signal. Gains of the I signal and the Q signal extracted by thefilter 232 are adjusted, and the I signal and the Q signal are outputfrom the RF IC 221.

The ADC 217 in the baseband IC 211 performs AD conversion of the inputsignal from the RF IC 221. More specifically, the ADC 217 converts the Isignal to a digital I signal and converts the Q signal to a digital Qsignal. Note that a single system signal may be received withoutperforming quadrature demodulation.

When a plurality of antennas are provided, the number of provided ADCsmay correspond to the number of antennas. Based on the digital I signaland the digital Q signal, the baseband circuit 212 executes a process ofthe physical layer and the like, such as demodulation process, errorcorrecting code process, and process of physical header, and obtains aframe. The baseband circuit 212 applies a process of the MAC layer tothe frame. Note that the baseband circuit 212 may be configured toexecute a process of TCP/IP when the TCP/IP is implemented.

The baseband circuit 212 or the CPU 215 may execute a process regardingthe MIMO. The baseband circuit 212 or the CPU 215 may execute at leastone or a plurality of a process of propagation path estimation, atransmission weight calculation process, a separation process of stream,and the like. The baseband circuit 212 or the CPU 215 may control theoperation of the filters 222 and 232 to extract signals covered by aused channel according to the setting of the channel. Another controllerthat controls the filters 222 and 232 may exist, and the basebandcircuit 212 or the CPU 215 may issue an instruction to the controller toperform similar control.

Fourth Embodiment

FIG. 24(A) and FIG. 24(B) are perspective views of wireless terminalaccording to the fourth embodiment. The wireless terminal in FIG. 24(A)is a notebook PC 301 and the wireless communication device (or awireless device) in FIG. 24(B) is a mobile terminal 321. Each of themcorresponds to one form of a terminal (which may indicate a basestation). The notebook PC 301 and the mobile terminal 321 are equippedwith wireless communication devices 305 and 315, respectively. Thewireless communication device provided in a terminal (which may indicatea base station) which has been described above can be used as thewireless communication devices 305 and 315. A wireless terminal carryinga wireless communication device is not limited to notebook PCs andmobile terminals. For example, it can be installed in a TV, a digitalcamera, a wearable device, a tablet, a smart phone, a gaming device, anetwork storage device, a monitor, a digital audio player, a web camera,a video camera, a projector, a navigation system, an external adapter,an internal adapter, a set top box, a gateway, a printer server, amobile access point, a router, an enterprise/service provider accesspoint, a portable device, a handheld device and so on.

Moreover, a wireless communication device installed in a terminal (whichmay indicate a base station) can also be provided in a memory card. FIG.25 illustrates an example of a wireless communication device mounted ona memory card. A memory card 331 contains a wireless communicationdevice 355 and a body case 332. The memory card 331 uses the wirelesscommunication device 355 for wireless communication with externaldevices. Here, in FIG. 25 , the description of other installed elements(for example, a memory, and so on) in the memory card 331 is omitted.

Fifth Embodiment

In the fifth embodiment, a bus, a processor unit and an externalinterface unit are provided in addition to the configuration of thewireless communication device according to any of the above embodiments.The processor unit and the external interface unit are connected with anexternal memory (a buffer) through the bus. A firmware operates theprocessor unit. Thus, by adopting a configuration in which the firmwareis included in the wireless communication device, the functions of thewireless communication device can be easily changed by rewriting thefirmware. The processing unit in which the firmware operates may be aprocessor that performs the process of the communication controllingdevice or the control unit according to the present embodiment, or maybe another processor that performs a process relating to extending oraltering the functions of the process of the communication controllingdevice or the control unit. The processing unit in which the firmwareoperates may be included in the access point or the wireless terminalaccording to the present embodiment. Alternatively, the processing unitmay be included in the integrated circuit of the wireless communicationdevice installed in the access point, or in the integrated circuit ofthe wireless communication device installed in the wireless terminal.

Sixth Embodiment

In the sixth embodiment, a clock generating unit is provided in additionto the configuration of the wireless communication device according toany of the above embodiments. The clock generating unit generates aclock and outputs the clock from an output terminal to the exterior ofthe wireless communication device. Thus, by outputting to the exteriorthe clock generated inside the wireless communication device andoperating the host by the clock output to the exterior, it is possibleto operate the host and the wireless communication device in asynchronized manner.

Seventh Embodiment

In the seventh embodiment, a power source unit, a power sourcecontrolling unit and a wireless power feeding unit are included inaddition to the configuration of the wireless communication deviceaccording to any of the above embodiments. The power supply controllingunit is connected to the power source unit and to the wireless powerfeeding unit, and performs control to select a power source to besupplied to the wireless communication device. Thus, by adopting aconfiguration in which the power source is included in the wirelesscommunication device, power consumption reduction operations thatcontrol the power source are possible.

Eighth Embodiment

In the eighth embodiment, a SIM card is added to the configuration ofthe wireless communication device according to the above embodiments.For example, the SIM card is connected with the MAC processing unit 10,the MAC/PHY management unit 60 or the controlling unit 112 in thewireless communication device. Thus, by adopting a configuration inwhich the SIM card is included in the wireless communication device,authentication processing can be easily performed.

Ninth Embodiment

In the ninth embodiment, a video image compressing/decompressing unit isadded to the configuration of the wireless communication deviceaccording to any of the above embodiments. The video imagecompressing/decompressing unit is connected to the bus. Thus, byadopting a configuration in which the video imagecompressing/decompressing unit is included in the wireless communicationdevice, transmitting a compressed video image and decompressing areceived compressed video image can be easily done.

Tenth Embodiment

In the tenth embodiment, an LED unit is added to the configuration ofthe wireless communication device according to any of the aboveembodiments. For example, the LED unit is connected to at least one ofthe MAC processing unit 10, the MAC/PHY management unit 60, thetransmission processing circuit 113, the reception processing circuit114 and the controlling circuit 112. Thus, by adopting a configurationin which the LED unit is included in the wireless communication device,notifying the operation state of the wireless communication device tothe user can be easily done.

Eleventh Embodiment

In the eleventh embodiment, a vibrator unit is included in addition tothe configuration of the wireless communication device according to anyof the above embodiments. For example, the vibrator unit is connected toat least one of the MAC processing unit 10, the MAC/PHY management unit60, the transmission processing circuit 113, the reception processingcircuit 114 and the controlling circuit 112. Thus, by adopting aconfiguration in which the vibrator unit is included in the wirelesscommunication device, notifying the operation state of the wirelesscommunication device to the user can be easily done.

Twelfth Embodiment

In a twelfth embodiment, the configuration of the wireless communicationdevice includes a display in addition to the configuration of thewireless communication device (the wireless communication device of theterminal (which may indicate the base station) according to any one ofthe above embodiments. The display may be connected to the MACprocessing unit of the wireless communication device via a bus (notshown). As seen from the above, the configuration including the displayto display the operation state of the wireless communication device onthe display allows the operation status of the wireless communicationdevice to be easily notified to a user.

Thirteenth Embodiment

In the present embodiment, [1] the frame type in the wirelesscommunication system, [2] a technique of disconnection between wirelesscommunication devices, [3] an access scheme of a wireless LAN system and[4] a frame interval of a wireless LAN are described.

[1] Frame Type in Communication System

Generally, as mentioned above, frames treated on a wireless accessprotocol in a wireless communication system are roughly divided intothree types of the data frame, the management frame and the controlframe. These types are normally shown in a header part which is commonlyprovided to frames. As a display method of the frame type, three typesmay be distinguished in one field or may be distinguished by acombination of two fields. In the IEEE 802.11 standard, identificationof a frame type is made based on two fields of Type and Subtype in theFrame Control field in the header part of the MAC frame. The Type fieldis one for generally classifying frames into a data frame, a managementframe, or a control frame and the Subtype field is one for identifyingmore detailed type in each of the classified frame types such as abeacon frame belonging to the management frame.

The management frame is a frame used to manage a physical communicationlink with a different wireless communication device. For example, thereare a frame used to perform communication setting with the differentwireless communication device or a frame to release communication link(that is, to disconnect the connection), and a frame related to thepower save operation in the wireless communication device.

The data frame is a frame to transmit data generated in the wirelesscommunication device to the different wireless communication deviceafter a physical communication link with the different wirelesscommunication device is established. The data is generated in a higherlayer of the present embodiment and generated by, for example, a user'soperation.

The control frame is a frame used to perform control at the time oftransmission and reception (exchange) of the data frame with thedifferent wireless communication device. A response frame transmittedfor the acknowledgment in a case where the wireless communication devicereceives the data frame or the management frame, belongs to the controlframe. The response frame is, for example, an ACK frame or a BlockACKframe. The RTS frame and the CTS frame are also the control frame.

These three types of frames are subjected to processing based on thenecessity in the physical layer and then transmitted as physical packetsvia an antenna. In IEEE 802.11 standard (including the extended standardsuch as IEEE Std 802.11ac-2013), an association process is defined asone procedure for connection establishment. The association requestframe and the association response frame which are used in the procedureare a management frame. Since the association request frame and theassociation response frame is the management frame transmitted in aunicast scheme, the frames causes the wireless communication terminal inthe receiving side to transmit an ACK frame being a response frame. TheACK frame is a control frame as described in the above.

[2] Technique of Disconnection Between Wireless Communication Devices

For disconnection, there are an explicit technique and an implicittechnique. As the explicit technique, a frame to disconnect any one ofthe connected wireless communication devices is transmitted. This framecorresponds to Deauthentication frame defined in IEEE 802.11 standardand is classified into the management frame. The frame for disconnectionmay be referred to as “release frame” by the meaning of releasingconnection, for example. Normally, it is determined that the connectionis disconnected at the timing of transmitting the release frame in awireless communication device on the side to transmit the release frameand at the timing of receiving the release frame in a wirelesscommunication device on the side to receive the release frame.Afterward, it returns to the initial state in a communication phase, forexample, a state to search for a wireless communication device of thecommunicating partner. In a case that the wireless communication basestation disconnects with a wireless communication terminal, for example,the base station deletes information on the wireless communicationdevice from a connection management table if the base station holds theconnection management table for managing wireless communicationterminals which entries into the BSS of the base station-self. Forexample, in a case that the base station assigns an AID to each wirelesscommunication terminal which entries into the BSS at the time when thebase station permitted each wireless communication terminal to connectto the base station-self in the association process, the base stationdeletes the held information related to the AID of the wirelesscommunication terminal disconnected with the base station and mayrelease the AID to assign it to another wireless communication devicewhich newly entries into the BSS.

On the other hand, as the implicit technique, it is determined that theconnection state is disconnected in a case where frame transmission(transmission of a data frame and management frame or transmission of aresponse frame with respect to a frame transmitted by the subjectdevice) is not detected from a wireless communication device of theconnection partner which has established the connection for a certainperiod. Such a technique is provided because, in a state where it isdetermined that the connection is disconnected as mentioned above, astate is considered where the physical wireless link cannot be secured,for example, the communication distance to the wireless communicationdevice of the connection destination is separated and the radio signalscannot be received or decoded. That is, it is because the reception ofthe release frame cannot be expected.

As a specific example to determine the disconnection of connection in animplicit method, a timer is used. For example, at the time oftransmitting a data frame that requests an acknowledgment responseframe, a first timer (for example, a retransmission timer for a dataframe) that limits the retransmission period of the frame is activated,and, if the acknowledgement response frame to the frame is not receiveduntil the expiration of the first timer (that is, until a desiredretransmission period passes), retransmission is performed. When theacknowledgment response frame to the frame is received, the first timeris stopped.

On the other hand, when the acknowledgment response frame is notreceived and the first timer expires, for example, a management frame toconfirm whether a wireless communication device of a connection partneris still present (in a communication range) (in other words, whether awireless link is secured) is transmitted, and, at the same time, asecond timer (for example, a retransmission timer for the managementframe) to limit the retransmission period of the frame is activated.Similarly to the first timer, even in the second timer, retransmissionis performed if an acknowledgment response frame to the frame is notreceived until the second timer expires, and it is determined that theconnection is disconnected when the second timer expires.

Alternatively, a third timer is activated when a frame is received froma wireless communication device of the connection partner, the thirdtimer is stopped every time the frame is newly received from thewireless communication device of the connection partner, and it isactivated from the initial value again. When the third timer expires,similarly to the above, a management frame to confirm whether thewireless communication device of the connection party is still present(in a communication range) (in other words, whether a wireless link issecured) is transmitted, and, at the same time, a second timer (forexample, a retransmission timer for the management frame) to limit theretransmission period of the frame is activated. Even in this case,retransmission is performed if an acknowledgment response frame to theframe is not received until the second timer expires, and it isdetermined that the connection is disconnected when the second timerexpires. The latter management frame to confirm whether the wirelesscommunication device of the connection partner is still present maydiffer from the management frame in the former case. Moreover, regardingthe timer to limit the retransmission of the management frame in thelatter case, although the same one as that in the former case is used asthe second timer, a different timer may be used.

[3] Access Scheme of Wireless LAN System

For example, there is a wireless LAN system with an assumption ofcommunication or competition with a plurality of wireless communicationdevices. CSMA/CA is set as the basis of an access scheme in theIEEE802.11 (including an extension standard or the like) wireless LAN.In a scheme in which transmission by a certain wireless communicationdevice is grasped and transmission is performed after a fixed time fromthe transmission end, simultaneous transmission is performed in theplurality of wireless communication devices that grasp the transmissionby the wireless communication device, and, as a result, radio signalscollide and frame transmission fails. By grasping the transmission bythe certain wireless communication device and waiting for a random timefrom the transmission end, transmission by the plurality of wirelesscommunication devices that grasp the transmission by the wirelesscommunication device stochastically disperses. Therefore, if the numberof wireless communication devices in which the earliest time in a randomtime is subtracted is one, frame transmission by the wirelesscommunication device succeeds and it is possible to prevent framecollision. Since the acquisition of the transmission right based on therandom value becomes impartial between the plurality of wirelesscommunication devices, it can say that a scheme adopting CarrierAvoidance is a suitable scheme to share a radio medium between theplurality of wireless communication devices.

[4] Frame Interval of Wireless LAN

The frame interval of the IEEE802.11 wireless LAN is described. Thereare several types of frame intervals used in the IEEE802.11 wirelessLAN, such as distributed coordination function interframe space (DIFS),arbitration interframe space (AIFS), point coordination functioninterframe space (PIFS), short interframe space (SIFS), extendedinterframe space (EIFS) and reduced interframe space (RIFS).

The definition of the frame interval is defined as a continuous periodthat should confirm and open the carrier sensing idle beforetransmission in the IEEE802.11 wireless LAN, and a strict period from aprevious frame is not discussed. Therefore, the definition is followedin the explanation of the IEEE802.11 wireless LAN system. In theIEEE802.11 wireless LAN, a waiting time at the time of random accessbased on CSMA/CA is assumed to be the sum of a fixed time and a randomtime, and it can say that such a definition is made to clarify the fixedtime.

DIFS and AIFS are frame intervals used when trying the frame exchangestart in a contention period that competes with other wirelesscommunication devices on the basis of CSMA/CA. DIFS is used in a casewhere priority according to the traffic type is not distinguished, AIFSis used in a case where priority by traffic identifier (TID) isprovided.

Since operation is similar between DIFS and AIFS, an explanation belowwill mainly use AIFS. In the IEEE802.11 wireless LAN, access controlincluding the start of frame exchange in the MAC layer is performed. Inaddition, in a case where QoS (Quality of Service) is supported whendata is transferred from a higher layer, the traffic type is notifiedtogether with the data, and the data is classified for the priority atthe time of access on the basis of the traffic type. The class at thetime of this access is referred to as “access category (AC)”. Therefore,the value of AIFS is provided every access category.

PIFS denotes a frame interval to enable access which is morepreferential than other competing wireless communication devices, andthe period is shorter than the values of DIFS and AIFS. SIFS denotes aframe interval which can be used in a case where frame exchangecontinues in a burst manner at the time of transmission of a controlframe of a response system or after the access right is acquired once.EIFS denotes a frame interval caused when frame reception fails (whenthe received frame is determined to be error).

RIFS denotes a frame interval which can be used in a case where aplurality of frames are consecutively transmitted to the same wirelesscommunication device in a burst manner after the access right isacquired once, and a response frame from a wireless communication deviceof the transmission partner is not requested while RIFS is used.

Here, FIG. 26 illustrates one example of frame exchange in a competitiveperiod based on the random access in the IEEE802.11 wireless LAN.

When a transmission request of a data frame (W_DATA1) is generated in acertain wireless communication device, a case is assumed where it isrecognized that a medium is busy (busy medium) as a result of carriersensing. In this case, AIFS of a fixed time is set from the time pointat which the carrier sensing becomes idle, and, when a random time(random backoff) is set afterward, data frame W_DATA1 is transmitted tothe communicating partner.

The random time is acquired by multiplying a slot time by a pseudorandominteger led from uniform distribution between contention windows (CW)given by integers from 0. Here, what multiplies CW by the slot time isreferred to as “CW time width”. The initial value of CW is given byCWmin, and the value of CW is increased up to CWmax everyretransmission. Similarly to AIFS, both CWmin and CWmax have valuesevery access category. In a wireless communication device oftransmission destination of W_DATA1, when reception of the data framesucceeds, a response frame (W_ACK1) is transmitted after SIFS from thereception end time point. If it is within a transmission burst timelimit when W_ACK1 is received, the wireless communication device thattransmits W_DATA1 can transmit the next frame (for example, W_DATA2)after SIFS.

Although AIFS, DIFS, PIFS and EIFS are functions between SIFS and theslot-time, SIFS and the slot time are defined every physical layer.Moreover, although parameters whose values being set according to eachaccess category, such as AIFS, CWmin and CWmax, can be set independentlyby a communication group (which is a basic service set (BSS) in theIEEE802.11 wireless LAN), the default values are defined.

For example, in the definition of 802.11ac, with an assumption that SIFSis 16 μs and the slot time is 9 μs, and thereby PIFS is 25 μs, DIFS is34 μs, the default value of the frame interval of an access category ofBACKGROUND (AC_BK) in AIFS is 79 μs, the default value of the frameinterval of BEST EFFORT (AC_BE) is 43 μs, the default value of the frameinterval between VIDEO(AC_VI) and VOICE(AC_VO) is 34 μs, and the defaultvalues of CWmin and CWmax are 31 and 1023 in AC_BK and AC_BE, 15 and 31in AC_VI and 7 and 15 in AC_VO. Here, EIFS denotes the sum of SIFS,DIFS, and the time length of a response frame transmitted at the lowestmandatory physical rate. In the wireless communication device which caneffectively takes EIFS, it may estimate an occupation time length of aPHY packet conveying a response frame directed to a PHY packet due towhich the EIFS is caused and calculates a sum of SIFS, DIFS and theestimated time to take the EIFS.

The terms used in each embodiment should be interpreted broadly. Forexample, the term “processor” may encompass a general purpose processor,a central processing unit (CPU), a microprocessor, a digital signalprocessor (DSP), a controller, a microcontroller, a state machine, andso on. According to circumstances, a “processor” may refer to anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), and a programmable logic device (PLD), etc. The term“processor” may refer to a combination of processing devices such as aplurality of microprocessors, a combination of a DSP and amicroprocessor, or one or more microprocessors in conjunction with a DSPcore.

As another example, the term “memory” may encompass any electroniccomponent which can store electronic information. The “memory” may referto various types of media such as a random access memory (RAM), aread-only memory (ROM), a programmable read-only memory (PROM), anerasable programmable read only memory (EPROM), an electrically erasablePROM (EEPROM), a non-volatile random access memory (NVRAM), a flashmemory, and a magnetic or optical data storage, which are readable by aprocessor. It can be said that the memory electronically communicateswith a processor if the processor read and/or write information for thememory. The memory may be arranged within a processor and also in thiscase, it can be said that the memory electronically communication withthe processor. The term “circuitry” may refer to not only electriccircuits or a system of circuits used in a device but also a singleelectric circuit or a part of the single electric circuit.

Note that the frames described in the embodiments may indicate not onlythings called frames in, for example, the IEEE 802.11 standard, but alsothings called packets, such as Null Data Packets. When it is expressedthat the base station transmits or receives a plurality of frames or aplurality of X-th frames, the frames or the X-th frames may be the same(for example, the same type or the same content) or may be different. Anarbitrary value can be put into X according to the situation. Theplurality of frames or the plurality of X-th frames may be transmittedor received at the same time or may be transmitted or received attemporally different timings. When it is expressed that a first frame, asecond frame, and the like are transmitted or received at temporallydifferent points, the expression of the first, the second, and the likeis just an expression for distinguishing the frames, and the types andthe content of the frames may be the same or different.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

The invention claimed is:
 1. A wireless communication system comprising:a wireless communication device, first wireless communication terminals,and second wireless communication terminals; wherein the wirelesscommunication device comprises a transmitter configured to transmit afirst frame including at least one pair of a first field and a secondfield corresponding to the first field, wherein one of a first groupidentifier or a second group identifier is selectively set in the firstfield of the at least one pair, the first group identifier indicatingthe first wireless communication terminals which have been associatedwith the wireless communication device, the second group identifierindicating the second wireless communication terminals which have notbeen associated with the wireless communication device, and whereinfirst information to designate a resource unit for random access is setin the second field corresponding to the first field in which the firstgroup identifier or the second group identifier is set, and wherein thefirst frame triggers that: each first wireless communication terminal ofthe first wireless communication terminals if the each first wirelesscommunication terminal has data for uplink transmission, determines afirst counted value by counting a number of first fields in which thefirst group identifier is set, determines a first subtracted value bysubtracting the determined first counted value from a randomly selectedfirst counter, and determines whether the each first wirelesscommunication terminal has a right to select a resource unit based onthe first subtracted value, in response to determining that the eachfirst wireless communication terminal has the right to select a resourceunit, randomly selects a first resource unit from the resource unitspecified in the second field corresponding to the first field of the atleast one pair in which the first group identifier is set, and transmitsa second frame via the randomly selected first resource unit in a fixedtime after the first frame is received, and each second wirelesscommunication terminal of the second wireless communication terminals ifthe each second wireless communication terminal has data for uplinktransmission, determines a second counted value by counting a number offirst fields in which the second group identifier is set, determines asecond subtracted value by subtracting the determined second countedvalue from a randomly selected second counter, and determines whetherthe each second wireless communication terminal has a right to select aresource unit based on the second subtracted value, in response todetermining that the each second wireless communication terminal has theright to select a resource unit, randomly selects a second resource unitfrom the resource unit specified in the second field corresponding tothe first field of the at least one pair in which the second groupidentifier is set, and transmits a third frame via the randomly selectedsecond resource unit in a fixed time after the first frame is received;and wherein the wireless communication device comprises a receiverconfigured to receive at least one second frame or at least one thirdframe, transmitted in response to the first frame.
 2. The wirelesscommunication device system according to claim 1, wherein the each firstwireless communication terminal determines whether the each firstwireless communication terminal has the right to select a resource unitbased on comparison between the first subtracted value and apredetermined value, and the each second wireless communicationterminals determines whether the each second wireless communicationterminal has the right to select a resource unit based on comparisonbetween the second subtracted value and a predetermined value.
 3. Thewireless communication system according to claim 1, wherein a terminalidentifier of one of the first wireless communication terminals isselectively set in the first field of the at least one pair, secondinformation to designate a resource unit for the first wirelesscommunication terminal having the terminal identifier is set in thesecond field corresponding to the first field in which the terminalidentifier is set, and the first frame allows the first wirelesscommunication terminal having the terminal identifier specified in thefirst field to transmit the second frame via the resource unitdesignated in the second field corresponding to the first field in whichthe terminal identifier is set.
 4. The wireless communication systemaccording to claim 3, wherein the first group identifier and the secondgroup identifier are selected from AIDs (Association IDs) other thanAIDs allowed to assign to wireless communication terminals among AIDsdefined in IEEE 802.11 standard, and the AIDs of the first groupidentifier and the second group identifier are different from eachother, and the terminal identifier is selected from the AIDs allowed toassign to wireless communication terminals among AIDs defined in IEEE802.11 standard.
 5. The wireless communication system according to claim4, wherein the AIDs of the first group identifier and the second groupidentifier are selected from among 0 and values larger than
 2007. 6. Thewireless communication system according to claim 1, wherein the eachfirst wireless communication terminal determines whether the each firstwireless communication terminal has a right to select a resource unit ifthe each first wireless communication terminal have data for uplinktransmission and if at least one first field in which the first groupidentifier is set is included in the first frame, and the each secondwireless communication terminal determines whether the each secondwireless communication terminal has a right to select a resource unit ifthe each second wireless communication terminal has data for uplinktransmission and if at least one first field in which the second groupidentifier is set is included in the first frame.
 7. The wirelesscommunication system according to claim 1, wherein the wirelesscommunication device communicates according to IEEE 802.11 standard, theeach first wireless communication terminal is a wireless communicationterminal having been assigned an AID (Association ID) by the wirelesscommunication device, and the each second wireless communicationterminals is a wireless communication terminal having not been assignedan AID by the wireless communication device.
 8. The wirelesscommunication system according to claim 1, wherein the wirelesscommunication device comprises at least one antenna.
 9. The wirelesscommunication system according to claim 1, wherein the wirelesscommunication device is configured to be a base station.
 10. A wirelesscommunication method, comprising: transmitting, by a wirelesscommunication device, a first frame including at least one pair of afirst field and a second field corresponding to the first field, whereinone of a first group identifier or a second group identifier isselectively set in the first field of the at least one pair, the firstgroup identifier indicating first wireless communication terminals whichhave been associated with the wireless communication device, the secondgroup identifier indicating second wireless communication terminalswhich have not been associated with the wireless communication device,and wherein first information to designate a resource unit for randomaccess is set in the second field corresponding to the first field inwhich the first group identifier or the second group identifier is set,wherein the first frame triggers that each first wireless communicationterminal of the first wireless communication terminals if the each firstwireless communication terminal has data for uplink transmission,determines a first counted value by counting a number of first fields inwhich the first group identifier is set, determines a first subtractedvalue by subtracting the determined first counted value from a randomlyselected first counter, and determines whether the each first wirelesscommunication terminal has a right to select a resource unit based onthe first subtracted value, in response to determining that the eachfirst wireless communication terminal has the right to select a resourceunit, randomly selects a first resource unit from the resource unitspecified in the second field corresponding to the first field of the atleast one pair in which the first group identifier is set, and transmitsa second frame via the randomly selected the resource unit in a fixedtime after the first frame is received, and each second wirelesscommunication terminal of the second wireless communication terminals ifthe each second wireless communication terminal has data for uplinktransmission, determines a second counted value by counting a number offirst fields in which the second group identifier is set, determines asecond subtracted value by subtracting the determined second countedvalue from a randomly selected second counter, and determines whetherthe each second wireless communication terminal has a right to select aresource unit based on the second subtracted value, in response todetermining that the each second wireless communication terminal has theright to select a resource unit, randomly selects a second resource unitfrom the resource unit specified in the second field corresponding tothe first field of the at least one pair in which the second groupidentifier is set, and transmits a third frame via the randomly selectedsecond resource unit in a fixed time after the first frame is received;and receiving, by the wireless communication device, at least one secondframe or at least one third frame, transmitted in response to the firstframe.
 11. A wireless communication device comprising: a receiverconfigured to receive a first frame including at least one pair of afirst field and a second field corresponding to the first field, whereinone of a first group identifier or a second group identifier isselectively set in the first field of the at least one pair, the firstgroup identifier indicating first wireless communication terminals whichhave been associated with a base station, the second group identifierindicating second wireless communication terminals which have not beenassociated with the base station, and wherein first information todesignate a resource unit for random access is set in the second fieldcorresponding to the first field in which the first group identifier orthe second group identifier is set; controlling circuitry configured tospecify at least one first field in which the second group identifier isset from the at least one pair if the wireless communication device hasnot been associated with the base station and if the wirelesscommunication device has data for uplink transmission, specify at leastone first field in which the first group identifier is set from the atleast one pair if the wireless communication device has been associatedwith the base station and if the wireless communication device has datafor uplink transmission, if a wireless communication terminal has datafor uplink transmission, determines a counted value by counting a numberof first fields in which the first group identifier is set, determines asubtracted value by subtracting the determined counted value from arandomly selected counter, and determine whether the wirelesscommunication terminal has a right to select a resource unit based onthe subtracted value, and in response to determining that the wirelesscommunication terminal has the right to select a resource unit, randomlyselect a resource unit from at least one resource unit specified in atleast one second field corresponding to the at least one first fieldspecified; and a transmitter configured to transmit a second frame viathe randomly selected resource unit in a fixed time after the firstframe is received.
 12. The wireless communication device according toclaim 11, wherein the controlling circuitry is configured to determinewhether the wireless communication terminal has the right to select aresource unit based on comparison between the subtracted value and apredetermined value.
 13. The wireless communication device according toclaim 11, wherein a terminal identifier of one of the first wirelesscommunication terminals is selectively set in the first field of the atleast one pair, second information to designate a resource unit for thefirst wireless communication terminal having the terminal identifier ofthe one of the first wireless communication terminals is set in thesecond field corresponding to the first field in which the terminalidentifier of the one of the first wireless communication terminals isset, the controlling circuitry is configured to check whether anidentifier of the wireless communication device is identical to theterminal identifier included in the first field of the at least one pairin the first frame if the wireless communication device has data foruplink transmission, and the transmitter is configured to transmit thesecond frame via the resource unit designated in the second fieldcorresponding to the first field in which the terminal identifieridentical to the identifier of the wireless communication device is set.14. The wireless communication device according to claim 11, wherein thewireless communication device communicates according to IEEE 802.11standard, each of the first wireless communication terminals is awireless communication terminal having been assigned an AID (AssociationID) by the base station, and each of the second wireless communicationterminal is a wireless communication terminal having not been assignedan AID by the base station.
 15. The wireless communication deviceaccording to claim 14, wherein the first group identifier and the secondgroup identifier are selected from AIDs other than AIDs allowed toassign to wireless communication terminals having been associated withthe base station among AIDs defined in IEEE 802.11 standard, and theAIDs of the first group identifier and the second group identifier aredifferent from each other.
 16. The wireless communication deviceaccording to claim 15 wherein the AIDs of the first group identifier andthe second group identifier are selected from among 0 and values largerthan
 2007. 17. The wireless communication device according to claim 11,further comprising at least one antenna.